Showing papers in "Lwt - Food Science and Technology in 1996"

Prolongation of the Shelf-life of Perishable Food Products using Biodegradable Films and Coatings

Abstract: The improvement of the safety and quality of minimally processed foods is of major interest to both the consumer and the food industry and is the topic of an EU-sponsored research project with nine international partners. The project optimizes existing techniques and in addition develops novel technologies to ensure high quality and safe food products. Among the systems studied is Modified Atmosphere Packaging, for which the available packaging film materials are tailored to the specific demands of the food products. A novelty in the project is the development of biodegradable packaging materials that can replace conventional synthetic materials. Additionally, edible coatings that are applied directly on the food surface are designed which create a modified atmosphere. The edible coatings can be furnished with active compounds such as antimicrobials or antioxidants to obtain additional desired effects. Such packagings and coatings may protect very powerfully against microbial spoilage and loss of intrinsic product quality, resulting in a prolonged shelf-life. An overview of the development and application of edible films and coatings is given here, comprising recent results from the EU project with regard to the barrier properties of edible films and the inclusion of active compounds.

Antioxidant Activity of Barley and Malt: Relationship with Phenolic Content

Abstract: One way to naturally inhibit the oxidative deterioration of beer would involve protecting the antioxidants present in barley (mainly polyphenols) during the malting process. Depending on the variety, the antioxidant activity of barley is not negligible. Its relationship with the content of the three main phenolic groups (flavan-3-ols, hydroxycinnamic derivatives and flavonols), determined by a new ultraviolet spectrophotometric method, is proposed. It increases during malting probably not only by the modification or releasing of phenolic compounds, but also by the formation of new antioxidants, such as Maillard reaction products.

Mango peels as a new tropical fibre: preparation and characterization

Abstract: In this study, isolation and characterization of mango peel dietary fibre were investigated. Fresh mango peels, obtained as a byproduct of syrup production, were successively wet-milled, washed with water and dried. A peel particle size of 15 mm in wet milling and a washing time of 5 min were found to remove soluble sugars and to increase total polyphenols and soluble dietary fibre content. Mango peel dietary fibre contained high amounts of total extractable polyphenols (70 g/kg) and soluble dietary fibre (281 g/kg) and had a high water-holding capacity (11·4 g/g dry matter). These characteristics indicated that mango peel is a good source of tropical fruit fibre.

Dynamics of oil uptake during deep-fat frying of potato slices

Abstract: The uptake of oil during deep-fat frying of potato slices was followed by frying slices for an equal length of time, introducing a fat-soluble and heat stable dye into the oil at different times before the end of frying and measuring the fraction of dyed oil compared to the total oil content. Total oil content was measured by a refractometric method, and the content of dyed oil by a spectrophotometric method. Results from these measurements were compared to those obtained by removing slices after various periods of frying and analysing fat content. The experiments with dyed oil showed conclusively that oil does not penetrate the potato slices during frying, but is taken up by the slice only when it is removed from the frying pan due to adhesion of oil to the surface of the slice. Therefore, oil uptake is primarily a surface phenomena involving an equilibrium between adhesion and drainage of oil upon retrieval of the slice from the oil bath.

The Effect of Extrusion Operating Conditions on the Apparent Viscosity and the Properties of Extrudates in Twin-Screw Extrusion Cooking of Maize Grits

Abstract: Maize grits were extrusion-cooked in a CM45 conical, counter-rotating twin screw extruder with varied feed rate (47 to 60 kg/h), product temperature (150 to 160°C), feed moisture content (13 to 17 g/100g wet basis), and die length (115 to 185 mm). The specific mechanical energy (SME), the starch gelatinizatiion degree, the apparent melt viscosity, the radial expansion ratio and extrudate bulk density were measured. The apparent viscosity, SME, and product properties, were found to be most dependent on the feed moisture content. Increasing moisture content decreased the SME, the degree of gelatinization, the apparent viscosity, and the radial expansion ratio, giving products with greater density. The apparent viscosity was used in the modelling of the extrudate properties. The apparent viscosity was found to affect the radial expansion ratio but not the extrudate bulk density.

Mechanism of High Pressure Denaturation of Proteins

Abstract: High pressure denaturation of ovalbumin, bovine serum albumin (BSA) and β-lactoglobulin was assessed by spectrofluorometry, specific rotation analysis and differential scanning calorimetry (DSC), and compared with heat and chemical denaturation. In all cases the denaturation caused by high pressure was similar to that caused by the cleavage of hydrogen bonds with urea or guanidine hydrochloride.

The Sourdough Microflora. Characterization of Hetero- and Homofermentative Lactic Acid Bacteria, Yeasts and Their Interactions on the Basis of the Volatile Compounds Produced

Abstract: Eighty-seven strains (15 species) of sourdough lactic acid bacteria (homo- and hetero-fermentative) and yeasts were characterized and statistically discriminated on the basis of volatile compounds produced during sourdough fermentation. The species differed and, in general, the strains differed within the species. Heterofermentative LAB mainly produced ethylacetate with some alcohols and aldehydes, and homofermentative LAB synthetized diacetyl and other carbonyls, while iso-alcohols were produced by yeast fermentation. Lactobacillus brevis subsp. lindneri and Lactobacillus plantarum were the LAB with the most complete profiles. Sourdoughs started with bacterial associations were characterized by a more complete profile (integrations of hetero- and homo-fermentative volatile compounds) and by a decrease of the percentage amounts of the main products individually synthetized. In association with yeasts (with the exception of L. plantarum DC400 - Saccharomyces exiguus M14 association) both hetero- and homo-fermentative LAB enhanced the formation of the yeast volatile compounds. Mixed sourdough starters ( L. brevis subsp. lindneri CB1, L. plantarum DC400 and Saccharomyces cerevisiae 141 or S. exiguus M14) were selected to produce sourdoughs with different volatile compound profiles.

Expansion Characteristics of Extruded Corn Grits

Abstract: Yellow corn grits with 180 g/kg moisture content (dry basis) were extrusion cooked in a Brabender single-screw laboratory scale extruder with various combinations of barrel temperature (100–200 °C) and screw speed (80–200 rpm). Bulk densities, solid densities, expansion properties, and total, open and closed pore volumes were determined. Extrudate bulk density, measured by glass bead displacement, was highly correlated with the bulk density based on the actual dimensions of the extrudates. Overall and radial expansion increased with temperature and screw speed whereas axial expansion decreased. Axial expansion was affected mostly by surging. The pore volumes had an increasing trend with temperature and screw speed.

PCR-based DNA Analysis for the Identification and Characterization of Food Components

Abstract: Analysis of specific nucleic acids in food allows control laboratories to determine the presence or absence of certain ingredients in complex products or the identification of specific characteristics of single food components. These analyses are based on nucleic acids probes, including the polymerase chain reaction (PCR), which made the detection of minute amounts of degraded nucleic acids and their sequence determination possible. In this review, we describe the approaches that have been taken to detect low levels of contaminants such as wheat in dietary food for coeliac patients and pork meat or fat in sausages. In addition, these methods may also be used for the identification of meat or fish species and the recognition of genetically altered foods, including the FlavrSavr™ tomato. These examples indicate that a comprehensive description of food products based on the analysis of nucleic acids will be feasible.

Identification and Quantification of Potent Odorants Formed by Toasting of Wheat Bread

Abstract: Slices of wheat bread were toasted until a distinct intensity of brown colour was attained. Potent odorants formed were evaluated by aroma extract dilution analysis and gas chromatography/olfactometry of headspace samples. Compounds showing high dilution factors were quantified, and their aroma activity values (OAV, ratio of concentration to odour threshold) were calculated on the basis of their odour thresholds in starch. The roasty smelling 2-acetyl-1-pyrroline (I) showed the highest OAV followed by (E)-2-nonenal (II), 3-methylbutyric acid (III), 4-hydroxy-2,5-dimethyl-3 (2H)-furanone (IV), methional (V) and 2,3-butanedione. Formation of nine odorants (I to V among others) was measured in relation to the intensity of the brown colour. It was found that, at the beginning of toasting, (I) increased more rapidly in the bread slices than (IV) which was mainly produced at medium browning.

High Pressure Inactivation ofByssochlamys niveaAscospores and Other Heat Resistant Moulds

Abstract: The response of persistent and vegetative forms of the heat resistant moulds Byssochlamys nivea , Byssochlamys fulva , Eurotium ( Aspergillus fischeri ), Eupenicillium spp. and Paecilomyces spp. to a combined pressure–temperature treatment was investigated. All vegetative forms are inactivated by 300 MPa at 25°C. Except for B. nivea ascospores, all persistent forms are strongly reduced by treatment in the range of 300–600 MPa at 10 to 60°C. In this range B. fulva , Eurotium and Eupenicillium spp. show unexpected and individual pressure–temperature responses. B. nivea ascospores needed pressures above 600 MPa and temperatures above 60°C for inactivation in representative studies. pH has little influence on the inactivation rate while low water activities are inhibitory. Treatment of 700 MPa at 60°C sensitizes B. nivea ascospores to subsequent thermal treatment. In grape juice, the initial inactivation rate at 700 MPa and 70°C is higher than in physiological salt solution. Tissue damage to ascospores during pressure treatment are visible only after preparation for electron microscopy.

Utilization of Jojoba Oil for Deep-fat Frying of Foods

Abstract: Jojoba oil is a mixture of long chain esters comprising C18, C20, C22and C24monounsaturated acids and alcohols, but in particular two ester molecules containing 40 and 42 carbon atoms which make up to 80% of the oil. Five quality parameters of Jojoba oil were compared with cotton oil in time–temperature conditions simulating abusive industrial deep-fat frying. In four out of five quality criteria, namely, colour index, oxidation index, peroxide value and viscosity, Jojoba oil was found to be superior to cotton oil, while free fatty acids showed comparable low values, within the range expected, in industrial frying operations. Oil uptake of a deep-fried restructured potato product was significantly higher in Jojoba oil as compared to cotton oil. The enhanced stability during deep-fat frying of Jojoba oil could play a part in improving the shelf-life of fried foods.

Effect of High Pressure Treatments on Peroxidase Activity, Ascorbic Acid Content and Texture in Green Peas

Abstract: Ultra-high isostatic pressure treatment was applied to green peas in order to evaluate the possibility of using this process as an alternative to blanching. Different operative conditions (magnitude of pressure from 400 to 900 MPa and treatment times of 5 and 10 min) combination with a mild heat treatment at 60 °C were examined. The effects of these treatments on peroxidase enzyme activity, ascorbic acid content and texture were studied. While treatment times did not affect the parameters measured, increase in pressure resulted in a higher level of peroxidase inactivation and retention of ascorbic acid. Pressurized samples did not show differences in texture, although a significant reduction in firmness was observed with respect to fresh peas. Among the conditions tested, 900 MPa for 5 min gave the best results with respect to fresh peas (residual peroxidase activity adn ascorbic acid content 12 % and 82%, respectively), and also in comparison with results reported in the literature for the blanching process. These results demonstrate that ultra-high pressure is a promising technology for use as an alternative to blanching.

Minimally Processed Pomegranate Seeds

Abstract: Ready-to-eat pomegranate seeds were prepared and their quality attributes and appearance was followed during storage for 7 d under different conditions Quality attributes, titratable acidity, total soluble solids, L* values, absorbance at 510 nm (anthocyanin content) and absorbance at 446 nm (brown metabolites) were analysed Respiratory activity, appearance of the seeds (shriveling and browning), and weight loss were also evaluated The influence of different washing treatments, storage temperatures (8, 4 and 1 °C) and actively or passively modified atmosphere packaging on the quality of the minimally processed pomegranate seeds was studied Washing the seeds with chlorine and chlorine followed by ascorbic and citric acid were selected, and storage at 1 °C led to the best quality preservation The best overall results were obtained for seeds washed with chlorine (100 mg/kg) plus antioxidants (5 g/L ascorbic acid and 5 g/L citric acid), and sealed in oriented polypropylene film using an initial atmosphere actively modified to 20 mL/L O 2 and 0 mL/L CO 2 Under these conditions, minimally processed pomegranate seeds maintained good quality and appearance for 7 d of storage at 1 °C without fungal attacks or off-flavour development

Surface Pasteurization of Raw Poultry Meat by Steam

Abstract: A device to surface pasteurize meat without producing a cooked appearance was built and tested. When inoculated with 10 7 Listeria inocua organisms, contamination levels on poultry meat samples were reduced to 10 3 organisms by treatment with steam to 140°C for 50 ms. The extraordinary rapidity of heating was achieved by condensing pure, thermally saturated steam onto the meat surface in the absence of noncondensible gases. Equally rapid surface cooling was then achieved by re-evaporating the condensate on the meat surface back into a vacuum. The best killing was achieved when treatments were repeated. This avoided the shadowing effect of the steel mesh cage which held the meat. The meat surface afforded some protection to the bacteria, compared to a paper surface. The rapidity of the process shows that a practical model could keep up with poultry slaughter line speeds. Such a model, including a sterile wrapping step, is suggested for poultry pieces and cut meats.

Kinetics of Osmotic Dehydration under Vacuum

Abstract: Osmotic dehydration under vacuum was studied. The effect of vacuum application was explained on the basis of the diffusional osmotic transport parameter, the mass transfer coefficient and interfacial area. A mathematical model is proposed to explain the mechanism of water transport during osmotic dehydration based on a more fundamental parameter, the osmotic pressure. Osmotic pressure ratios were calculated for dehydration under atmospheric conditions and under vacuum. The increased osmotic pressure due to vacuum application was also calculated. The rate of mass transfer during osmotic dehydration of food increases under vacuum. The vacuum applied affects only the rate at which the equilibrium is attained and not the equilibrium osmotic pressureper se.

Identification ofListeria innocuaas a Biological Indicator for Inactivation ofL. monocytogenesby some Meat Processing Treatments

Abstract: Four strains of Listeria monocytogenes and two strains of L. innocua were studied for their response to heat, gamma radiation, lactic acid and sodium nitrite treatments generally used in the meat industry. Listeria spp., when heated in 10% meat homogenate at 75 °C, showed a phenomenal tailing effect with a thermal death time of 1 min. The D 10 value (dose required for 10% survival) of Listeria spp. to gamma radiation in phosphate buffer at –40 °C was observed to be higher (0.3 kGy) than at 0 °C (0.15 kGy), whereas the protection offered by 10% meat homogenate did not vary with change in irradiation temperature (D 10 = 0.5 kGy at 0 ° and −40 °C). While 1.25 g/L lactic acid in brain heart infusion (BHI) or meat homogenate was bacteriostatic, a higher concentration 1.25 g/L was bactericidal to both Listeria spp. The combined effect of 1.25 g/L lactic acid 10 g/L NaCl was also bactericidal. Growth inhibition of Listeria spp. by either lactic acid or NaNO 2 at low pH was also demonstrated. The overall response of both Listeria spp. to these processing treatments were comparable suggesting possible use of L. innocuua in lieu of L. monocytogene for the safe evaluation of processes used in the meat industry to control potentially hazardous L. monocytogenes .

Effects of High Pressure on the Physico-chemical Characteristics of Dairy Creams and Model Oil/Water Emulsions

Abstract: A pasteurized liquid dairy cream (pH 6.7–6.8; 350 g/kg fat) was not significantly modified by high pressure processing (HPP) at 450 MPa and 25 °C for 15–30 min, or at 10 °C for 30 min, from the physical standpoint of fat globule size distribution and flow behaviour. Physical stability was also unchanged, in spite of some fat globule aggregation, upon HPP at 450 MPa and 40 °C for 30 min. With a UHT sterilized dairy cream (pH 6.7; 350 g/kg fat), HPP induced formation of fat globule aggregates and markedly increased viscosity, whether carried out at 450 MPa and 25 °C for 15 or 30 min, or at 10 or 40 °C for 30 min. This aggregation was partly reversed during chilled storage. Both types of creams remained physically stable for 8 d at 4 °C, without any phase separation. When the pasteurized cream was first held at 60 °C to melt fat crystals, then processed at 25 °C and 450 MPa for 30 min, an extensive formation of fat crystals was observed in the fat globules by cryofracture and SEM, as previously reported by other authors. Model liquid oil/water emulsions of pH 7.0, containing 50 g/kg sodium caseinate and 300 g/kg peanut oil or glycerol trioleate were processed at 450 MPa and 10, 25 or 40 °C for 30 min, without changes in droplet size distribution or emulsion viscosity. No droplet coalescence or aggregation was observed. Emulsions with the same composition, except with s-lactoglobulin as an emulsifying agent and stabilizer in place of sodium caseinate, were also processed at 450 MPa and 10 or 25 °C for 30 min, without any changes in oil droplet size. However, HPP at 450 MPa and 25 °C for 30 min increased emulsion viscosity, while gelled emulsions were formed upon HPP at 450 MPa and 40 °C for 30 min. The viscosity of emulsions pressurized at 25 °C further increased during chilled storage, and was higher for emulsions with peanut oil than with triolein. Hence, HPP at 450 MPa for 30 min did not break down or coalesce oil droplets in any of the model emulsions, but did change the rheology of emulsions stabilized by a pressure-sensitive protein (s-lactoglobulin). It may thus become possible to induce desirable texture modifications in specific food, pharmaceutical or cosmetic emulsions, simultaneously to microbial inactivation.

Changes in Surface Composition of Spray-Dried Food Powders due to Lactose Crystallization

Abstract: The surface composition of spray-dried lactose-containing powders was estimated by electron spectroscopy for chemical analysis (ESCA), and particle structure was studied by scanning electron microscopy before and after storage in a humid atmosphere. The surface composition of dry powders made from lactose/sodium caseinate solutions was nearly identical to that of powders stored at 75% relative humidity for 4 d. Protein started to dominate the powder surface even when it was present at only low solution concentrations. The particle structure after storage in a humid atmosphere was completely changed even though the surface composition remained relatively unchanged. When soybean oil emulsions with sodium caseinate and lactose were spray-dried, protein was over-represented on the powder surface. If the protein concentration was sufficiently high, the fat was almost completely encapsulated. In the case of the powders with high lactose content almost total release of encapsulated fat on the powder surface was observed after storage in a humid atmosphere. When the lactose concentration was lower, release of fat on the powder surface was less pronounced. The structure of fat-containing powders was studied by scanning electron microscopy. Before storage in a humid atmosphere, particles were discrete with smooth surfaces. As the fat was released onto the powder surface, the powder became highly agglomerated and attained a smooth structure.

Shelf-life extension of cottage cheese by modified atmosphere packaging.

Abstract: The effectiveness of flushing headspace of commercial packages of cottage cheese with pure carbon dioxide on shelf-life extension was evaluated. An optimum headspace of about 25% (v/v) in 250 mL packages, flushed with pure CO 2 , extended shelf-life of cottage cheese at 8 °C by about 150% without altering sensory properties or causing any other negative effect. Flushing of headspace with pure CO 2 caused dissolution of about 8 mmol/kg CO 2 which gave additional protection, besides good sanitation, against spoilage bacteria, yeasts and moulds. In order to maintain the proper CO 2 level in headspace and cause its dissolution into the product the use of high barrier packaging materials is essential.

Evidence for Protein–Tannin Interaction in Legumes: Implications in the Antioxidant Properties of Faba Bean Tannins

Abstract: The nutritional consequence of the absence of tannins in faba bean and lentil seeds was evaluated by comparing tannin-containing and tannin-free varieties for in vitro protein digestibility, cystine chemical reactivity and extent of proteolysis. In vitro protein digestibility and cystine reactivity (susceptibility to reduction) were found to be significantly increased in the tannin-free compared to the tannin-containing variety. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis of faba bean and lentil proteins, before and after proteolytic digestion, showed that proteins in the tannin-free variety underwent better digestion than those in the tannin-containing variety of the same species. This suggested that interaction between tannin and protein impaired the susceptibility of seed proteins to proteolysis. Preliminary evaluation of the antioxidant properties of faba bean tannins indicated that the antioxidant activity found is accounted for by the direct interaction of tannin with hydroxyl radical rather than to a metal chelating activity. On the basis of these data it is possible to hypothesise that, in spite of the known adverse action on protein digestibility, legume seed tannings might exert a beneficial nutritional antioxidant activity.

Influence of process variables on the characteristics of a high moisture fish soy protein mix texturized by extrusion cooking

Abstract: A two level factorial experimental design was used to study the influence of process variables (feed rate, 33 – 38 kg/h; screw speed, 70 – 100 rpm; extruder barrel temperature, 173 – 177 °C; feed moisture, 630 – 650 g/kg) on the resistance to stretching, colour and final water content (after immersion in water) of extrudates from a mix of fish surimi and soy protein concentrate texturized by extrusion cooking. The relationship between process variables and system parameters (product temperature before the cooling die, mean and peak residence times in the extruder + die) was also investigated. Extrusion cooking was carried out on a long barrel (1500 mm) corotative twin screw extruder equiped with an 800 × 40 × 3 mm cooling die. Extrudate texture was found to depend mainly on feed moisture, screw speed and barrel temperature, in this decreasing order. Extrudate colour depended most significantly on feed moisture and barrel temperature, while the final water content of extrudates (after immersion in water) was most affected by barrel temperature and screw speed. Within the experimental domain, the feed rate and mean residence time had no significant effect on the characteristics of extrudates.

The Effect of pH on the Relationship Between Hydrophilic/Lipophilic Characteristics and Emulsification Properties of Soy Proteins

Abstract: Hydrophilic characteristics of four soybean protein isolates, determined through measurement of spontaneous water absorption capacity (WAC), were greatly affected by pH in the range of 2 to 7. While minimum WAC was apparent near the isoelectric region and increased away from the pI (isoelectric point) for most isolates, a partially hydrolysed soy protein isolate behaved the opposite way. Lipophilic characteristics, determined as the spontaneous oil absorption capacity (OAC), varied up to 120% as pH changed. The balance between hydrophile and lipophile (WOAI), calculated as the ratio between WAC and OAC, showed a response to pH similar to WAC, with a minimum value near the pI, except for the hydrolysed isolate. Emulsifying capacity (EC) was maximum near the pI. However, the hydrolysed isolate showed a greater EC, reaching a maximum at pH 3, which could be attributed to peptides of different size and net charge with no single pI. As the hydrophilic/lipophilic balance reached lower values as a result of the effect of pH, EC increased, suggesting that a relatively high hydrophobicity is needed to enhance the EC of soy proteins. The effect of pH on emulsion stability was opposite to that shown on EC, except for the hydrolysed isolate, as maximum instability was apparent near the pI, where electrostatic and steric repulsions between oil droplets are highly decreased. The effect of pH on emulsion stability was closely related to WAC and indicated that a high hydration of the interfacial film is necessary for increasing stability against creaming and flocculation.

Osmotic Dehydration Kinetics of Pineapple Wedges using Palm Sugar

Abstract: Osmotic dehydration kinetics of pineapple wedges was studied using palm sugar at different syrup concentration and temperature. Equilibrium kinetics were presented by defining equilibrium constants and nonequilibrium period of water loss and solid gain followed the model based on mass balance and zero order reaction kinetics. At constant temperature, the rate constants for both water and solids increased with increase in syrup concentration. At constant syrup concentration, the rate constants of water increased and the rate constants of solid decreased with the increase of temperature. Temperature had much more effect at high syrup concentration.

Encapsulation of Orange Peel Oil by Co-crystallization

Abstract: Orange peel oil was microencapsulated by co-crystallization. Encapsulation capacity of sucrose syrups was found to be greater than 90% for a range of 100 to 250 g oil/kg of sugar. Surface oil, a measurement of encapsulation efficiency, varied from 3350 to 8880 mg oil/kg solids. Moisture content of the crystals was lower than 10 g/kg and bulk density was greater than 670 kg/m3for all the co-crystallizates prepared. Sensory evaluation showed that all of the panelists were able to detect oxidized flavours in oils without antioxidant added after storage at 35 °C for 1 d. When BHA was added to the oil prior to co-crystallization, no signs of oxidized flavours were detected after 2 months of storage at ambient temperature.

A Study of Factors Affecting Wine Volatile Composition and its Application in Discriminant Analysis

Abstract: Seventy-two young commercial Spanish wines from the 1990 harvest were analysed during the first semester of 1991. Analytical data on 52 volatile compounds were obtained. Diverse multivariate analysis methods were utilized to study these data in order to obtain a factorization so that an interpretation of the role played by grape variety and origin could be made. Cluster analysis showed similar aroma profiles according to site or grape variety, and a strong influence of the presence of skins during fermentation. Discriminant analysis has shown that wine volatile composition contains enough information to establish a consistent control of authenticity, allowing the assessment of the origin or grape variety of very different wine samples through a common function. Origin and grape variety are two interactive factors that strongly influence wine volatile composition. Origin affects mainly the amount and proportion of compounds derived from unsaturated lipid in the grape and volatile derived from yeast aminoacid, while grape variety affects mainly this latter group of compounds.

Machine Vision System for Automated Detection of Stained Pistachio Nuts

Abstract: A machine vision system was developed to separate stained pistachio nuts, which comprise about 5% of the California crop, from unstained nuts. Stained nuts have lower consumer acceptance and higher incidences of aflatoxin contamination. The machine vision system may be used as an automated quality control device to detect stained nuts. The system was tested on three different pistachio process streams: the bichromatic colour sorter reject stream (floaters and sinkers) and the manually sorted small nut shelling stock stream (floaters). The system had a minimum overall error rates of 13% for the sinker bichromatic reject stream, 14% for the floater bichromatic sorter reject stream and 15% for the floater small shelling stock stream.

Influence of packaging treatments on the keeping quality of 'Salinas' lettuce

Abstract: Heads of lettuce ( Lactuca sativa L., cv. ‘Salinas’) were individually wrapped or sealed in nonoriented perforated (22 μm thickness) or unperforated (25 or 50 μm thickness) new polypropylene (PP) films, and stored for 2 weeks at 2 °C plus 2·5 d at 12 °C. Vacuum cooling and/or active modification of the atmosphere within the package by flushing a gas mixture were applied. Quality of lettuce by scoring wilting, physiological disorders, bacterial decay and overall visual quality was determined. In naked heads stored in air and in lettuce wrapped in perforated PP, russet spotting and pink rib, the main disorders of lettuce during postharvest, developed. However, in all treatments with sealed PP bags, these disorders practically did not appear. Heart leaf injury and brown stain developed on lettuce sealed in PP bags, particularly after transfer to higher temperature. Pink rib and heart leaf injury mainly appeared in vacuum cooled lettuce. The reason for this susceptibility, that has not been previously reported, is unknown and additional research is needed to identify the factors involved. Low O 2 was related with high quality score. The best results were obtained in vacuum cooled lettuce packed in PP bags with initial 21·6 g/L O 2 and 0 g/L CO 2 atmosphere.

Effects of purified endo-β-xylanase and endo-β-glucanase on the structural and baking characteristics of rye doughs

Abstract: The importance of arabinoxylans and b-glucans in rye baking was studied by depolymerizing these cell wall polysaccharides in situ with purified xylanase and β-glucanase. Two different rye cultivars, Danko (from Sweden) and Muskate (from Canada), were used. The most marked effect of the enzymes was the reduction in proofing time, with xylanase having the greater effect. Xylanase addition made the doughs soft and slack, as indicated by the viscoelastic measurements. Both xylanase and β-glucanase had a positive effect on the dough volume, but a negative effect on the oven rise. Addition of increasing levels of β-glucanase during baking degraded β-glucans extensively in the bread but did not influence the content or solubility of arabinoxylans. Microstructural studies showed xylanase addition to cause increased fragmentation of cell walls. Xylanase also increased the release of amylose from the starch granules. At high dosage of xylanase swelling of the starch granules and a release of proteins from aleurone cells were observed. Sugar analysis and NMR studies of soluble non-starch polysaccharides isolated from the bread revealed higher contents of soluble arabinose, xylose and glucose residues in the Danko bread without enzyme addition than in the corresponding Muskate.

Textural Changes and Proteolysis of Low-Moisture Mozzarella Cheese Frozen under Various Conditions

Abstract: Hardness, adhesiveness, cohesiveness, springiness and nonprotein nitrogen (NPN) content were used to assess the effects of aging time (6 to 21 d at 4 °C), ripening before or after freezing, freezing rate and frozen storage (3 months at −20 °C) on characteristics of low-moisture Mozzarella cheese. The results obtained were compared with unfrozen control samples, aged at 4 °C for between 6 and 42 d. Freezing cheeses that had been ripened for about 14 d produced a product similar to refrigerated cheese at the same stage of aging. When cheese samples were frozen after 6 d of ripening, they were harder and the NPN content was greater than in refrigerated controls, even after aging the thawed samples for 8 more d.