Showing papers in "International Journal of Food Science and Technology in 2002"

Anti‐oxidant activity and total phenolic content of some Asian vegetables

Abstract: The anti-oxidant activity of extracts from 36 vegetables was evaluated by using a model system consisting of β-carotene and linoleic acid. The total phenolics of the extracts was determined spectrophotometrically according to the Folin–Ciocalteau procedure and ranged from 34 to 400 mg (100 g)−1 on a fresh weight basis. Mint, aonla, black carrots, chenopodium, fenugreek, kachnar and ginger had high phenolic contents. The anti-oxidant activity expressed as per percent inhibition of oxidation ranged from a high of 92% in turmeric extracts to a low of 12.8% in long melon. Other vegetables found to have high anti-oxidant activity (>70%) were kachnar, aonla, ginger, fenugreek, mint, beetroot, black carrots, Brussels sprouts, broccoli, lotus stem, yam, coriander and tomato. Anti-oxidant activity correlated significantly and positively with total phenolics (r2=0.6578, P < 0.05). The results indicate that vegetables containing high phenolics may provide a source of dietary anti-oxidants.

A review of modified atmosphere packaging of fish and fishery products – significance of microbial growth, activities and safety

Abstract: Modified atmosphere packaging (MAP) extends shelf-life of most fishery products by inhibiting bacterial growth and oxidative reactions. The achievable extension of shelf-life depends on species, fat content, initial microbial population, gas mixture, the ratio of gas volume to product volume, and most importantly, storage temperature. The shelf-life of fishery products is usually limited by microbial activity, although for some fatty fishes or at superchilled storage, it can be limited by nonmicrobial activity. Packaging of fishery products under modified atmospheres (MA) increases shelf-life compared with those packaged under air, but confers little or no additional shelf-life increase compared with vacuum packaging. The specific spoilage organism (SSO) of MA packaged cod at 0 °C has been found to be Photobacterium phosphoreum. Whether or not this bacterium is the general SSO for all marine temperate fishes at different storage temperatures and under various CO 2 /N 2 /O 2 mixtures needs to be resolved. Without proper control of storage temperature, the benefits of MAP may be lost. Higher temperatures inevitably lead to less dissolved CO 2 in the product and consequently loss of inhibitory effect, which may result in higher microbial and enzymatic activity, and uncertainties concerning the microbial safety, as food-borne pathogens might be present in the product.

A review of physical and chemical protein-gel induction

Abstract: Summary Protein gelation is important to obtain desirable sensory and textural structures in foods. Gelation phenomenon requires a driving force to unfold the native protein structure, followed by an aggregation retaining a certain degree of order in the matrix formed by association between protein strands. Protein gelation has been traditionally achieved by heating, but some physical and chemical processes form protein gels in an analogous way to heat-induction. A physical means, besides heat, is high pressure. Chemical means are acidification, enzymatic cross-linking, and use of salts and urea, causing modifications in protein–protein and protein–medium interactions. The characteristics of each gel are different and dependent upon factors like protein concentration, degree of denaturation caused by pH, temperature, ionic strength and/or pressure.

Minerals and phytic acid interactions: is it a real problem for human nutrition?

Abstract: Summary Because of its high density of negatively charged phosphate groups, phytic acid (PA) forms very stable complexes with mineral ions rendering them unavailable for intestinal uptake. Indeed, the first step in mineral absorption requires that the mineral remains in the ionic state. As the PA content of the diet increases, the intestinal absorption of zinc, iron and calcium decreases. The inhibitory effects of PA on magnesium or copper are more controversial. Nevertheless, PA does not occur alone in foods and is often consumed with various compounds. Phytates are always present in vegetal matrix composed of fibres, minerals, trace elements and other phytomicronutrients. Thus, in order to evaluate mineral absorption from phytate-rich products, all components of diet and food interactions should be considered and it is hard to predict mineral bioavailability in such products by using only the phytate content.

Composition and functional properties of rice

Abstract: Starch, protein and lipids are the main rice grain components that affect cooking and eating quality. An analysis of the literature indicates that rice of good eating quality shows the following characteristics: low amylose and low protein contents and large breakdown as measured by an amylograph. However, there are significant cultural differences in quality preferences and the most important acceptance factors for Asian consumers living in the United States are cooked rice appearance and aroma. This review examines the major constituents of rice (starch, lipid and protein) and their impact on eating quality as reflected by the functional properties of rice.

Molecular and catalytic properties of phytate‐degrading enzymes (phytases)

Abstract: Summary Phytate-degrading enzymes catalyse the step-wise release of phosphate from phytate, the principle storage form of phosphorus in plant seeds and pollen.They are widespread in nature, occurring in plants and micro-organisms, as well as in some animal tissues. Phytate-degrading enzymes have been studied intensively in recent years because of the great interest in such enzymes for reducing phytate content in animal feed and food for human consumption.Phytate-degrading enzymes are also of interest for producing defined breakdown products of phytate for kinetic and physiological studies.Certain myo-inositol phosphates have been proposed to have novel metabolic effects and therefore, the physiological role of different myo-inositol phosphates is presently undergoing extensive research.Generally, phytase behaves like a monomeric enzyme with molecular masses between 40 and 70 kDa.Up to now, two main types of phytate-degrading enzymes have been identified; acid phytate-degrading enzymes with an pH optimum around pH 5 and alkaline phytate-degrading enzymes with an pH optimum around pH 8.Most of the so far described phytate-degrading enzymes belong to the acidic type, and their optimal pH ranges from 4.5 to 6.0. This review summarises the molecular features as well as catalytic properties of phytate-degrading enzymes and also discusses enzymatic phytate degradation.

Comparison of wild and cultured gilthead sea bream (Sparus aurata); composition, appearance and seasonal variations

Abstract: Major quality parameters, such as muscle composition, fat deposition, muscle fatty acid composition and external appearance were studied in wild and cultured gilthead sea bream. Muscle fat content and total depot fat (peritoneal and perivisceral fat) indicated a seasonal variation with minimum values observed in late spring and maximum in late summer. Gonadosomatic indices of cultured fish were lower than those found in wild specimens. Lipid content of cultured sea bream was much higher than that of wild fish. Differences were also observed in fatty acid profiles. Cultured fish were characterized by higher levels of monoenes, n-9 and 18:2n-6 fatty acids and wild fish by higher levels of saturates, 20:4n-6, n-3 fatty acids and n-3/n-6 ratios. Differences were also noted in the external appearance of fish.

Basmati rice: a review

Abstract: India contributes about one-third of the world acreage under rice. Rice is available in over 5000 varieties, of which Basmati rice occupies a prime position on account of its extra long superfine slender grains, pleasant, exquisite aroma, fine cooking quality, sweet taste, soft texture, length-wise elongation with least breadth-wise swelling on cooking and tenderness of cooked rice. This article reviews the quality and aroma traits of Basmati rice, particularly the varieties grown in different parts of India and Pakistan, the agronomy, breeding and physiology of the grain, the trade scenario, Agmark grade designation for export and the US patent of new hybrid strains of Basmati.

Ultrasound decontamination of minimally processed fruits and vegetables

Abstract: Summary The effectiveness of power ultrasound for the microbial decontamination of minimally processed fruits and vegetables was studied. Reductions in Salmonella typhimurium attached to iceberg lettuce obtained by cleaning with water, chlorinated water, ultrasound with water and ultrasound with chlorinated water were 0.7, 1.7, 1.5 and 2.7 logs, respectively, for small-scale (2 L) trials. The cleaning action of cavitation appears to remove cells attached to the surface of fresh produce, rendering the pathogens more susceptible to the sanitizer. For large-scale (40 L) trials, the addition of chlorine to water in the tank gave a systematic difference in Escherichia coli decontamination efficiency. However, the frequency of ultrasound treatment (25, 32–40, 62–70 kHz) had no significant effect on decontamination efficiency (P > 0.69). With the potentially high capital expenditure together with the expensive process of optimization and water treatment, it is unlikely that the fresh produce industry would be willing to take up this technology. Furthermore, the additional one log reduction achieved by applying ultrasound to a chlorinated water wash does not completely eliminate the risk of pathogens on fresh produce.

Inhibitory activity of brown algal phlorotannins against hyaluronidase

Abstract: The inhibitory effect of brown algal phlorotannins on hyaluronidase was evaluated by an in vitro assay. Crude phlorotannins from the brown algae Eisenia bicyclis and Ecklonia kurome had a stronger inhibitory effect than well-known inhibitors such as catechins and sodium cromoglycate. IC 5 0 values of the following six phlorotannins: phloroglucinol, an unknown tetramer, eckol (a trimer), phlorofucofuroeckol A (a pentamer), dieckol and 8,8'-bieckol (hexamers), were 280, 650, > 800, 140, 120 and 40 μM, respectively. The IC 5 0 of catechin, epigallocatechin gallate and sodium cromoglycate was 620, 190 and 270 μM, respectively. 8,8'-Bieckol, the strongest HAase inhibitor in this study, acted as a competitive inhibitor with an inhibition constant (K i ) of 35 μM. Acetylation of the phlorotannins markedly decreased their inhibitory potency.

Sensory, chemical and microbiological assessment of farm-raised European sea bass (Dicentrarchus labrax) stored in melting ice

Abstract: Summary Farm raised European sea bass (Dicentrarchus labrax) were stored in melting ice for aperiod up to 22 days from the time of harvest, and sensory, chemical, and microbiologicalassessments were made at intervals. The storage life of the ungutted fish, determined bysensory evaluation of the cooked flesh, was 19 days. Of the chemical tests, only k 1 valueprovided a useful means of monitoring early storage change. Trimethylamine, total volatilebases and pH showed practically no change during the first half of the edible storage life ofthe fish. Changes in free fatty acid (FFA) content and thiobarbituric acid (TBA) valuecould not be used to determine loss of acceptability or end of storage life. Sulphideproducing bacteria constituted a very low proportion of the total aerobic flora, suggestingthat the common sulphide producer Shewanella putrefaciens was not a major spoiler of seabass in this trial.Keywords Composition, fish, freshness indicators, quality assessment. IntroductionThe farming of European sea bass (Dicentrarchuslabrax) is a fast growing aquaculture venture inmany Mediterranean countries. The white flesh,mild flavour and low fat content of sea bass aremajor attributes sought by the consumer.A review of the scientific and technical literaturerevealed some information about the compositionof European sea bass (Nicolosi et al., 1993;Amerio et al., 1996), and the effects of dietarylipid, protein, and carbohydrate levels on bodycomposition of growing fish (Ballestrazzi et al.,1994; Ballestrazzi & Lanari, 1996; Lanari et al.,1999). However, little information is available onquality changes occurring in European sea bassduring postharvest handling, distribution andretail display, or on the most effective methodsof assessing quality changes and storage stabilityof this marine species.Uchiyama & Kato (1974) and Chang et al.(1998) studied changes of Japanese sea bass(Lateolabrax japonicus) under partial freezingand refrigerated storage. Aoki et al. (1991) inves-tigated the proximate and fatty acid compositionof wild and cultured Japanese sea bass, andErickson (1992) studied the lipid and tocopherolcomposition of striped bass (Morone saxatilis)and hybrid striped bass (M. saxatilis · M. chrys-ops). Boyd et al. (1992) evaluated the storage lifeof hybrid striped bass under chillpack (–2 °C)and refrigerated (2 °C) storage conditions, andEifert et al. (1992) and Handumrongkul & Silva(1994) investigated effects of postharvest coolingand modified atmosphere packaging on the stor-age life of striped bass fillets. Karahadian et al.(1995) studied changes of stored commerciallygrown and wild-captured striped bass fillets, andFair et al. (1993) and Webster et al. (1995)examined effects of dietary lipid and proteinlevels on the growth and composition of hybridstriped bass.

Formation of sunflower oil emulsions stabilized by whey proteins with high-pressure homogenization (up to 350 MPa): effect of pressure on emulsion characteristics

Abstract: A new ultra-high-pressure homogenizer was used to make very fine oil in water emulsions. The effect of pressures up to 350 MPa on sunflower oil (20%) in water emulsions was studied. The emulsifier used was whey protein concentrate (1.5%). The properties of the emulsions were characterized by laser light scattering (droplet size distribution) and coaxial cylinders rheometry (rheological behaviour). The protein adsorption fraction was obtained by a spectrophotometric method using bicinchoninic acid reagent. Significant modifications in the structure and the texture of the emulsions were observed as the pressure increased. No change was revealed by polyacrylamide gel electrophoresis of the whey protein within the pressure range studied. Microdifferential scanning calorimetry scans indicated that the changes of the structural and textural properties may be because of changes in the protein conformation.

Anti-cancer function of phytic acid

Abstract: Inositol hexaphosphate (InsP 6 a.k.a. phytic acid or IP 6 ) is ubiquitous. In the plant kingdom it is particularly abundant in cereals and legumes; in much smaller amounts IP 6 and its lower phosphorylated forms (IP 1-5 ) are contained in most mammalian cells, where they are important in regulating vital cellular functions. Both in vivo and in vitro experiments have demonstrated striking anticancer (preventive as well as therapeutic) effects of IP 6 . Inositol also is anti-carcinogenic, albeit to a lesser extent; it acts synergistically IP 6 in inhibiting cancer. In addition to reduction in cell proliferation, IP 6 increases differentiation of malignant cells often resulting in reversion to the normal phenotype. IP 6 is quickly absorbed from the rat stomach and upper intestine and distributed as inositol and IP 1 . In vitro, it is instantaneously taken up by malignant cells undergoing variable dephosphorylation to inositol and IP 1-5 , pointing towards their role in mediating the action of IP 6 . In humans, IP 6 has recently been detected in urine, plasma and other biological fluids; the levels fluctuating with ingestion or deprivation of IP 6 or IP 6 -rich diet. As IP 6 is high in high-fibre diets, these also may explain, at least in part, the epidemiological observation showing the association of ingesting high-fibre diets with a lower incidence of certain cancers. Along with safety, the reproducible efficacy of IP 6 and inositol in the prevention of cancer in laboratory animals warrant their inclusion in our strategies for cancer prevention and perhaps therapy in humans. A side from the anticancer action, IP 6 and inositol also have numerous other health benefits. All these facts of normal physiological presence of IP 6 in our body the level of which fluctuates with intake, association of an IP 6 -rich diet with low incidence of several diseases and vice versa, and finally reversal of some of these conditions, at least in part, by IP 6 supplementation strongly argue in favour of its inclusion as an essential nutrient or perhaps a vitamin.

Phytic acid–trace element (Zn, Cu, Mn) interactions

Abstract: Summary Studies in animals and human subjects have shown that diets high in phytic acid can cause zinc deficiency, and that the phytate content is negatively correlated to zinc absorption. Suboptimal zinc status has been shown to cause increased morbidity, poor pregnancy outcome, impaired growth, immune competence and cognitive function, emphasizing the need to optimize zinc bioavailability. Reducing the content of phytate in the diet is one way of improving zinc absorption and this can be achieved by novel precipitation methods during processing, food preparation methods that activate endogenous phytase (e.g. baking, fermentation, malting and hydrothermal processing), or addition of exogenous phytase. During the action of phytase on phytic acid, the hexaphosphate is hydrolysed into inositol phosphates with lower degrees of phosphorylation. Because only the penta- and hexaphosphates have been shown to inhibit zinc absorption, it is often essential to analyze the individual forms of phytate in the diet when evaluating zinc bioavailability. Phytic acid does not inhibit copper absorption, but has a modest inhibitory effect on manganese absorption.

Phytogenic and microbial phytases in human nutrition

Abstract: Summary Phytate (inositol hexa phosphate) hydrolysis can occur during food preparation and production and in the intestine, either by phytase from plants, yeasts or other micro-organisms. This degradation is of nutritional importance, because removal of phosphate groups from the inositol ring results in an increased bioavailability of essential dietary minerals. To substantially improve iron absorption the degradation has to be virtually complete. Food processing techniques increasing the activity of the naturally occurring plant phytases are soaking, malting, hydrothermal treatment and fermentation. An alternative is addition of phytases or micro-organisms producing phytase. Phytate degradation in the stomach and small intestine occurs as a result of activity of dietary phytase of plant or microbial origin. The plant phytase is less stable than fungal phytase in the physiological conditions of the intestine. Biotechnologically produced phytases may be possible for use tomorrow in food processing as well as plant raw material and starter cultures with inserted phytase genes.

Effect of moderate electric field pulses on the diffusion coefficient of soluble substances from apple slices

Abstract: The effects of a moderate electric field pulse (MEFP) on the diffusion coefficient of soluble substances from apple slices have been investigated. The apparent diffusion coefficient, D, was studied for both thermally and electrically treated samples. For thermally treated samples, the variation of D th as a function of temperature followed an Arrhenius type kinetic with two diffusion regimes: (i) without thermal pretreatment (E a 28 kJ mole 1 ) and (ii) after plasmolysis pretreatment (E a 13 kJ mole 1 ). In the case of electrically treated samples, only one regime was observed, with an intermediate activation energy (E a 20 kJ mole 1 ). Furthermore, it was found that an electrical pretreatment with moderate temperature elevation (10 15 °C) combined with a low thermal treatment, significantly enhanced the diffusion coefficient (D e1 ) compared with reference values. For instance, after a standard MEFP treatment (500 V em 1 , 1000 pulses, 100 μs duration) D el was 3.9 x 10 10 m 2 s 1 at 20 °C compared with reference values of 2.5 and 4.4 x 10 10 m 2 s for untreated and denatured samples, respectively, and 13.4 x 10 10 m 2 s 1 at 75 °C compared with 10.2 x 10 10 m 2 s 1 for thermally denatured samples. This indicates that an electrical treatment has a greater effect on the structure and permeability of apple tissue than thermal treatment. Cette etude evalue l'effet d'impulsions de champ electrique modere sur la structure et la permeabilite des tissus de pomme en mesurant le coefficient de diffusion apparent de substances solubles de tranches de pomme. Tandis que les echantillons traites thermiquement exigent une denaturation complete (2mn a 75°C) pour montrer une diffusion de solute significative, ceux traites electriquement ne necessitent qu'une elevation de temperature moderee (10-15°C) pour un meme resultat.

Performance of virgin olive oil and vegetable shortening during domestic deep-frying and pan-frying of potatoes

Abstract: The performance of virgin olive oil and a commercial vegetable shortening was investigated during 10 successive pan-fryings of potatoes at 180 °C for a total period of 60 min and during 10 successive deep-fryings at 170 °C for a total period of 120 min. These are typical conditions of Greek domestic cooking. For both the oils tested the effect of pan-frying on K232, K268, K316, α-tocopherol, total polar artefacts, Rancimat induction times, octanoic acid formation and linoleic acid decomposition was worse than the effect of deep-frying on the same variables. The same was true for visible spectrum and total phenols in virgin olive oil. No systematic variations of oleic acid, refractive index and trans-isomers of fatty acids were detected. None of the oils reached the limit of 25-27% total polar artefacts. Both oils performed similarly during pan-frying, while virgin olive oil performed better during deep-frying. A very strong correlation between octanoic acid formation and total polar artefacts in the whole data set was observed.

In vitro properties of phytases from various microbial origins

Abstract: Summary For the evaluation of the effectiveness of phytase preparations as feed additive, in vitro properties like temperature optimum, temperature stability, pH optimum and pH profile or proteolytic stability are of utmost importance. Although at present all commercial phytase preparations authorized as feed additives in the EU are produced by recombinant filamentous fungi and have similar in vitro properties (acidic pH optimum, narrow pH range, low thermostability) the diversity of microbial phytases is great. Microbial sources for phytases span from fungi and yeasts to bacteria. Some of the naturally occurring phytases were identified to have high thermostability and a broad pH range (e.g. Aspergillus fumigatus phytase). The bacterial Bacillus phytases generally differ from other phytases, having a pH optimum from 7.0 to 8.0, being Ca2+ dependent and highly specific for phytate. Thermostability can considerably be increased by protein engineering. A so-called Consensus phytase encoded by a synthetic gene was found to be stable in aqueous solutions at 70 °C and in feed at pelleting temperatures of 80–90 °C. The rate and site of inactivation of feed enzymes in the digestive tract are determined by their susceptibility to proteolytic enzymes. Highest residual activities after incubation in the presence of pepsin or in supernatants of stomach digesta was observed for Escherichia coli and Consensus phytases, while the Bacillus phytase was found to be most resistant to pancreatin. Comparative studies on in vitro properties of enzymes intended for use as feed additives provide valuable information for prediction of in vivo effectiveness.

Sous vide cooked beef muscles: effects of low temperature-long time (LT-LT) treatments on their quality characteristics and storage stability

Abstract: Summary Beef muscles were sous vide cooked by applying different low temperature-long time treatments and changes in their physical properties were measured. The effects of selected treatments on pasteurization values and chilled storage stability were investigated. The results obtained indicated that cooking weight loss increased and shear force values decreased as the treatment temperature was raised from 50 to 65 � C, while processing times (90–360 min) did not have a significant effect on these variables. The colour parameter a was strongly affected by the different treatments. The pasteurization values obtained were enough to inactivate vegetative cells but were insufficient to achieve a significant reduction of Clostridium botulinum spores. The microbial quality of the product remained acceptable during the storage period. Over the storage time, thiobarbituric acid reactive substance (TBARS) numbers were significantly affected by the thermal treatment applied. Maximum TBARS values obtained were lower than those reported for meat processed without vacuum. Cooked beef flavours for all treatments decreased uniformly after 21 days of storage.

Biogenic amines formation in Atlantic herring (Clupea harengus) stored under modified atmosphere packaging using a rapid HPLC method

Abstract: A rapid high-performance liquid chromatographic (HPLC) method for the determination of nine biogenic amines and trimethylamine (TMA) was developed. A derivatization procedure is reported. It involves dissolving benzoyl chloride in acetonitrile to enhance its reaction with biogenic amines. This was compared with benzoyl chloride dissolved in methanol and with only benzoyl chloride to find the optimal condition for benzoylation of biogenic amines in terms of time and derivatization conditions. A gradient elution system was used for analysis with a mixture of acetonitrile and HPLC grade water and took less than 7 min to complete the analysis. The application of this method to detect biogenic amines in herring stored at 2 ± 2 °C and in modified atmosphere packing (MAP) was investigated. The concentrations of amines in herring held at 2 ± 2 °C increased more rapidly than herring stored in MAP. The level of TMA in herring held at 2 ± 2 °C was higher than herring stored in MAP. No significant differences were found in histamine concentrations between herring stored at 2 ± 2 °C and in MAP during the early stages of storage period but there was a significant difference (P < 0.05) after 6 days of storage. Significant differences were found (P < 0.05) in concentrations of putrescine (after 6 days) and cadaverine (after 4 days) between herring held at 2 ± 2 °C and in MAP.

Iron absorption and the iron-binding and anti-oxidant properties of phytic acid

Abstract: Summary Phytic acid present in cereals, legumes and oilseeds is usually regarded as an anti-nutritive factor. Its negative effects on the bioavailabilty of iron and other essential minerals and trace elements have been described in several studies in man and monogastric animals. Phytic acid and iron are thought to form insoluble complexes which are not available for absorption under the pH conditions of the small intestine. A number of recent studies have suggested that reducing the phytate content of foods by genetic modification or via the action of intrinsic or extrinsic phytases may have a beneficial impact on iron availability. Over the last decade potential beneficial effects of phytic acid have also been recognized. In vitro studies indicate that phytic acid acts as an anti-oxidant through its iron chelating properties. However, it is as yet uncertain whether physiological intakes of phytic acid can significantly improve the anti-oxidant status in man and animals.

Effect of genetically modified low phytic acid plants on mineral absorption

Abstract: Summary The reduction of phytic acid content in grains by genetic manipulation is a novel approach to increase mineral absorption from food based diets. Low phytic acid corn (Zea mays), rice (Oryza sativa), barley (Hordeum vulgare) and soybean (Gycine max) genotypes have been generated and mineral absorption has been evaluated. Genetically modified low phytic acid plants could be a novel contribution to the reduction of micronutrient malnutrition and animal waste phosphorus. Nevertheless, additional research needs to be done to understand the molecular biology and genetics of phytic acid accumulation during seed development, the negative and positive roles of dietary phytic acid in human health and the feasibility and effectiveness of the sustainable implementation of this approach at the community level.

Processing factors affecting the osmotic dehydration of diced green peppers

Abstract: Summary A2 5–2 fractionalfactorialdesignwasusedtoinvestigatetheeffectofsalt(2–10%),sorbitol(0–10%)concentration,agitation(0–80rpm),tissuetosolutionratio(1:3to1:6)andtemperature(20–50 C)onweightloss,solidsgain,saltandsorbitoluptake,wateractivity,tissuebrixandsolutionbrix,duringosmoticdehydration(OD)ofdicedgreenpeppersResultsshowedthatsaltandsorbitolconcentrationwerethemostsignificantfactorsInthefirsthalfhouroftheosmoticprocess,saltandsorbitolsignificantlyincreasedweightloss,solidsgainandtissuebrix,anddecreasedwateractivityTemperaturewasalsoasignificantfactorItincreasedweightlossduringthefirst2hoftheprocess,anddecreasedwateractivityafter20hofosmosisAgitationandtissuetosolutionratiowerelessimportantKeywords Fractionalfactorialdesign,osmosis,sorbitol,salt,temperature IntroductionDehydrationoffoodproductsbyosmosisinvolveswateroutflowfromtheproducttothesolution,solutetransferfromthesolutiontotheproductandleachingoutofproductsolutestothesolu-tionAcombinationofosmosis,diffusion,fluxinteractionsandshrinkageyieldsdehydrationOsmoticdehydration(OD)isusefulasapre-processingsteppriortodryingandfreezingfoods,includingfruitandvegetables,meatandseafoodproducts (Lerici etal, 1985; Quintero-Ramosetal, 1993; Collignan & Raoult-Wack, 1994)ThebeneficialeffectsofODincludehigherqualityofthefinalproductandlowerenergyrequirements(Panagiotouetal,1998)AsODisusuallydoneatmoderatetemperatures,waterisremovedfromtheproductwithoutanyphasechangeThisprovidesbetterretentionofvolatileflavoursandreducestissuedamagecomparedwithconventionalairandsundryingprocesses(Raoult-Wack,1994)SeveralfactorsaffecttheODprocess,inclu-dingthetypeandconcentrationoftheosmoticsolutions,processingtemperatureandtime,brinetotissueratio,rateofagitationandrawmaterialcharacteristics(Cunhaetal,2001)Ofthese,theeffectsofthetypeandconcentrationofosmoticsolutionshavebeenstudiedextensivelyDifferentsolutessuchassalt,sugarand/orhighfructosecornsyruphavebeenused,eitheraloneorincombina-tion,asosmoticagents(Lericietal,1985;BiswalLBiswalBQuintero-Ramosetal,1993;CollignanRTorregianietal,1995;Vijayanandetal,1995)Collignan&Raoult-Wack(1994)usedmixedsolutesofsalt,sugarandcornstarchsyrupasosmoticagentsinthedewateringandsaltingofcodTheyfoundthatcertaincombinationsofsolutesincreaseddewateringUseofsorbitolincombina-tionwithwheypermeateasanosmoticagentwassuggestedbyTorregianietal(1995)becauseofitsantibrowningandhumectantpropertiesLenart&Flink(1984)studiedtheeffectofosmotictempera-tureandtime,solutetype,solutionconcentrationandagitationontheosmoticbehaviourofpotatoTheyshowedthathighconcentrationsofsolutionandlongosmotictimesincreasedthepenetrationdepthofosmoticagentsanddecreasedthemoisturecontentofsamplesElevatedtemperaturesresulted

Substrate specificity, heat inactivation and inhibition of polyphenol oxidase from different aubergine cultivars

Abstract: The effects of substrate specificity, heat inactivation, temperature, pH and inhibitors on polyphenol oxidase (PPO) activity obtained from three different aubergine cultivars were investigated to identify the most appropriate aubergine cultivar for dried preparations. PPO obtained from different aubergine cultivars (cultivars I, II and III) was partially purified by (NH 4 ) 2 SO 4 precipitation followed by dialysis. PPO showed activity with catechol and 4-methylcatechol but not with L-tyrosine. The best substrate for cultivar I (V m a x : 3333.3 EU min - 1 mL - 1 , K m : 8.7 mM and V m a x /K m : 384.9 min - 1 ) and cultivar III (V m a x : 1000 EU min - 1 mL - 1 , K m : 9.3 mM and V m a x /K m : 107.5 min - 1 ) was catechol, but 4-methylcatechol was the best substrate for cultivar II (V m a x : 5000 EU min - 1 mL - 1 , K m : 35.5 mM and V m a x /K m : 140.8 min - 1 ). The optimum pH for aubergine PPO was 7.0 with catechol as a substrate and 6.0 with 4-methylcatechol. Heat inactivation studies showed a decrease in enzyme activity at temperatures above 40 °C. For catechol and 4-methylcatechol substrates, the optimum temperature for maximum PPO activity was 30 °C for all aubergine cultivars except cultivar I using catechol which was 20 °C. The effects of compounds such as tropolone, D,L-dithiothreitrol and glutathione as inhibitors of the reactions catalysed by PPO were tested. Generally, tropolone was the most effective inhibitor.

Effects of vegetable type and antimicrobial dipping on survival and growth of Listeria innocua and E. coli

Abstract: Summary The survival and growth of inoculated strains of Listeria innocua and Escherichia coli during storage on ready-to-use vegetables (lettuce, dry coleslaw mix) were examined. The effects of antimicrobial dipping treatments (100 ppm chlorine solution, 5 min, 1% citric acid solution, 5 min, 1% ascorbic acid, 5 min) on inoculated samples were also investigated. Populations of L. innocua and E. coli on undipped lettuce significantly increased (P < 0.05, by 1–1.5 log cycles), while populations on undipped coleslaw gradually decreased (P < 0.05) during a 14-day storage period at 8 °C. The efficacy of the disinfection treatments were dependent on vegetable type and its microbial load; they were more effective on lettuce than on coleslaw. In general, antimicrobial dipping of lettuce or coleslaw significantly reduced (P < 0.05) initial L. innocua, E. coli and total mesophilic populations but resulted in enhanced survival and/or growth during extended storage at 8 °C.

Involvement of pectolytic micro-organisms in coffee fermentation

Abstract: During the fermentation of Coffea arabica L., the most frequently found pectolytic bacteria were Erwinia herbicola and Klebsiella pneumoniae. These micro-organisms produce pectatelyase which is unable to depolymerize esterified pectins of mucilage without previous de-esterification. Furthermore, the optimal activities are observed at pH 8.5 whereas fermentation conditions are acidic (5.3-3.5). The major lactic acid bacteria, Leuconostoc mesenteroides, do not produce pectolytic enzymes. Only a Lactobacillus brevis strain, rarely isolated with a low frequency, shows a polygalacturonase activity compatible with fermentation conditions. Mucilage decomposition seems to be correlated to acidification and not to enzymatic pectolysis. Inoculation with pectolytic micro-organisms allows microbiological control of the fermentation but does not speed up the process. It would be preferable to use lactic acid bacteria so that the pH remained as close as possible to natural fermentation, where acidification is important. This practice would standardize the coffee fermentation microflora and therefore control the end product quality. (Resume d'auteur)

Alleviation of the adverse effect of cooking on sorghum protein digestibility through fermentation in traditional African porridges

Abstract: Cooking sorghum is well known to reduce its protein digestibility. In southern Africa fermented sorghum porridges are commonly consumed. Knowledge is lacking as to how their preparation affects sorghum protein digestibility. Five sorghum varieties of varied origin were fermented using traditional semi-solid state fermentation. In vitro protein digestibility and a new index, in vitro insoluble protein digestibility, were measured. Both increased during fermentation, generally within the first day, coinciding with a strong decrease in pH. The increase in insoluble protein digestibility suggests fermentation causes structural changes in the sorghum storage proteins (prolamins and glutelins), making them more accessible to pepsin attack. Wet cooking during porridge-making greatly reduced protein digestibility. Combining fermentation with cooking, either fermenting then cooking or cooking then fermenting, significantly improved protein digestibility over wet cooking alone. Thus natural fermentation, as applied in traditional African porridge preparation is an effective method of improving the protein digestibility of cooked sorghum.

Whey protein aggregation under shear conditions – effects of pH-value and removal of calcium

Abstract: The effects of pH-value and a reduction in calcium content on the kinetics of whey protein denaturation and the aggregation behaviour, under shear in a scraped surface heat exchanger, were examined. The denaturation rate of β-lactoglobulin at 80 °C is considerably retarded as the pH-value decreases from pH 6.7 to 4.5. Aggregates which are produced under shear between pH 4 and 5.5 reveal a small particle size (< 5 pm) irrespective of the lactose content and the heating temperature. This is attributed to the low reactivity of the thiol groups and the small net charge of the proteins in this pH-range. At a reduced calcium concentration the heat- and shear-treatment resulted in a gritty structure with large rubber-like particles. These are not to be taken as primary whey protein aggregates but as fragments of a fine-stranded gel.

Parboiling of rice. Part II: Effect of hot soaking time on the degree of starch gelatinization

Abstract: Summary A differential scanning calorimetric study was done on raw and parboiled rice to determine the degree of gelatinization. Unparboiled rice absorbed the highest amount of endothermic heat, the enthalpy change gradually decreasing with increasing hot soaking time. The highest degree of gelatinization was achieved when the paddy was soaked for 120 min at 80 � C. With increasing degree of gelatinization, the yield point in a compression test also increased. During the parboiling process internal fissures were healed, resulting in higher head rice yield during milling.