Colour is an important quality attribute in the food and bioprocess industries, and it influences consumer’s choice and preferences. Food colour is governed by the chemical, biochemical, microbial and physical changes which occur during growth, maturation, postharvest handling and processing. Colour measurement of food products has been used as an indirect measure of other quality attributes such as flavour and contents of pigments because it is simpler, faster and correlates well with other physicochemical properties. This review discusses the techniques and procedures for the measurement and analysis of colour in food and other biomaterial materials. It focuses on the instrumental (objective) and visual (subjective) measurements for quantifying colour attributes and highlights the range of primary and derived objective colour indices used to characterise the maturity and quality of a wide range of food products and beverages. Different approaches applied to model food colour are described, including reaction mechanisms, response surface methodology and others based on probabilistic and non-isothermal kinetics. Colour is one of the most widely measured product quality attributes in postharvest handling and in the food processing research and industry. Apart from differences in instrumentation, colour measurements are often reported based on different colour indices even for the same product, making it difficult to compare results in the literature. There is a need for standardisation to improve the traceability and transferability of measurements. The correlation between colour and other sensory quality attributes is well established, but future prospects exist in the application of objective non-destructive colour measurement in predictive modelling of the nutritional quality of fresh and processed food products.

Colour Measurement and Analysis in Fresh and Processed Foods: A Review

Mathematical modeling of thin layer solar drying of sultana grapes

In this study, a solar cabinet dryer consisting of a solar air heater and a drying cabinet, was used in drying experiments. Pumpkin, green pepper, stuffed pepper, green bean, and onion were dried in thin layers. Three different drying air velocities were applied to the process of drying to determine their effects on drying time. Fresh materials were dried by a natural sun drying method. In order to explain drying curves of these products different moisture ratio models were performed and evaluated based on their determination coefficients (R2). Our results revealed that drying air temperature could increase up to about 46°C. Drying air velocity had an important effect on drying process. Drying time changed between 30.29 and 90.43 hours for different vegetables by the solar drying. This drying time was between 48.59 and 121.81 hours for the natural sun drying. Drying curves could be explained by determined thin layer drying models satisfactorily with very high determination coeffcients.

Thin layer solar drying of some vegetables

Natural fibers today are a popular choice for applications in composite manufacturing. Based on the sustainability benefits, biofibers such as plant fibers are replacing synthetic fibers in composites. These fibers are used to manufacture several biocomposites. The chemical composition and properties of each of the fibers changes, which demands the detailed comparison of these fibers. The reinforcement potential of natural fibers and their properties have been described in numerous papers. Today, high performance biocomposites are produced from several years of research. Plant fibers, particularly bast and leaf, find applications in automotive industries. While most of the other fibers are explored in lab scales they have not yet found large-scale commercial applications. It is necessary to also consider other fibers such as ones made from seed (coir) and animals (chicken feather) as they are secondary or made from waste products. Few plant fibers such as bast fibers are often reviewed briefly but other p...

A Review of Natural Fibers Used in Biocomposites: Plant, Animal and Regenerated Cellulose Fibers

Mathematical modeling of thin layer drying of pistachio by using solar energy

Solar drying - an effective means of food preservation

A rapid method for quantitative determination of beta-carotene, including cis-isomers, in dried mango has been developed. Applicability of available methods to dried products was limited because of formation of artifacts caused by extraction and preparation. The analytical procedure was based on the extraction of carotenoids from dried mango mesocarp using a mixture of methanol and acetone/hexane, allowing the separation of disturbing fibers. No saponification was required. Furthermore, carotenoid determination by HPLC on a C30 stationary phase was achieved. This method was applied to determine beta-carotene and its stereoisomers in fresh, dried, and solar-dried mango slices of four cultivars. Drying resulted in a complete and partial degradation of xanthophylls and all-trans-beta-carotene, respectively. Isomerization was shown to depend on the drying process. Whereas conventionally dried mangoes were characterized by elevated amounts of 13-cis-beta-carotene, solar-dried mango slices contained additional amounts of the 9-cis-isomer. Calculation of vitamin A values was based on the real amount of the beta-carotene stereoisomers and ranged from 113 to 420 and from 425 to 1010 RE/100 g for fresh and dried mango slices, respectively.

Quantitative determination of beta-carotene stereoisomers in fresh, dried, and solar-dried mangoes (Mangifera indica L.).

Experimental investigation of the performance of the solar tunnel dryer for drying bananas

An optimum drying routine for producing non-sulphited mango slices has been developed The interaction of essential drying parameters (air temperature, air velocity, dew point, slice thickness and drying time) on water activity ( a W ) and browning was determined Microbiological stability of the dried product was achieved at a moisture content of 17% wet base (wb) corresponding to a W  = 06 Browning was monitored by the red colour shade of the product (CIE-Lab chromaticity coordinate a *) Drying air temperature and drying time were shown to be the primary factors influencing product colour and a W  In contrast to common practice, drying for about 6 h at elevated air temperature (80 °C), instead of 50 or 60 °C for a longer time, was optimal, since significant colour changes of the mango slices were not observed even without the use of any chemical or thermal pre-treatment Moreover, at increased temperature, drying time was considerably shortened from about 9 h to 6 h, resulting in significant extension of the drying capacity Industrial Relevance The suggested process concept for dried mango slices based on high-temperature drying is of utmost significance for the international marketing of dried fruit products Chemical pre-treatments such as sulphitation often used to minimise quality deficiencies could be avoided Sulphitation has been recently under critical consideration with respect to allergen labelling of foodstuffs implemented by EU-Member States in November 2004 (Directive 2003/89/EC) [Directive 2003/89/EC Official Journal of the European Union, 25112003, pp L308/15–18 ( http://europaeuint/eur-lex/pri/en/oj/dat/2003/l_308/l_30820031125en00150018pdf )] Export quality was improved and the drying process simplified, improving the utilisation of drying capacities Particularly referring to an application of the technology in small- and medium-sized enterprises with limited investment possibilities, the suggested novel drying procedure in mango processing aimed at the optimisation of well-established simple drying methods instead of choosing technically more sophisticated technologies

W. Mühlbauer

Papers

Solar drying - an effective means of food preservation

Quantitative determination of beta-carotene stereoisomers in fresh, dried, and solar-dried mangoes (Mangifera indica L.).

Experimental investigation of the performance of the solar tunnel dryer for drying bananas

Quality improvement of non-sulphited mango slices by drying at high temperatures

Drying characteristics of copra and quality of copra and coconut oil