LITERATURE DATA OF HEAT TRANSFER COEFFICIENTS IN FOOD PROCESSING

ABSTRACT

Published data on the surface heat transfer coefficients in food processing operations have been selected from the literature, organized into a database, and presented. Useful information concerning the proposed equation, the system geometry, the experimental conditions, the range of application, and the relevant references, are tabulated.     

EVALUATION OF STORAGE STABILITY OF HOP PELLETS BY CHEMILUMINESCENCE ANALYSIS

Chemiluminescence (CL) produced in hop pellets of Saazer, Hallertau Hersbrucker, Tettnanger, and Lublin was detected using the single photoelectron counting system. When the hop pellet was analyzed at 80°C, the CL intensity increased, reached a maximum, and then decreased. The CL intensity of the hop pellets increased with storage time and showed a good relationship with the loss of (α+β) acids in the staling hop pellets. It was also thought that the deterioration rate of the hop pellets could be evaluated by observing the CL producing pattern of the fresh ones before storage. It was, therefore, expected that the CL analysis might be a useful technique for a quality check of the hop pellets.     

HEAT TRANSFER COEFFICIENT IN FOOD PROCESSING: COMPILATION OF LITERATURE DATA

ABSTRACT

Heat transfer coefficient data in food processing were retrieved from literature and classified per process and material. Most of the data were available in the form of empirical equations using dimensionless numbers. All available empirical equations were transformed in the form of Heat Transfer Factor vs. Reynolds Number (j_H=aReⁿ). In the case when more than one equation reported for the same process and material, a new similar equation was fitted to consolidate the existing literature equations. It is expected that the resulting equations are more representative and predict more accurately the heat transfer coefficients. Average equations for each process are also proposed.     

MASS TRANSFER COEFFICIENT IN FOOD PROCESSING: COMPILATION OF LITERATURE DATA

Mass transfer coefficient data in food processing were retrieved from literature and classified per process and material. Most of the data were available in the form of empirical equations using dimensionless numbers. All available empirical equations were transformed in the form of mass transfer factor versus Reynolds number (j_M = a Re ⁿ ). Average equations for each process are also proposed.     

COMPUTER-AIDED PREDICTIONS OF FOOD STORAGE STABILITY: OXIDATIVE DETERIORATION OF A SHRIMP PRODUCT

ABSTRACT— A study was conducted on stability of a freeze-dried shrimp bar packaged in various materials. The purpose of this study was to develop a method for predicting the storage stability of dry foods stored in semipermeable containers and deteriorating through oxidation of lipids. In the shrimp bar, organoleptic deterioration was correlated with absorption of oxygen and with loss of carotenoid pigment; these indices of oxidation were used for the study. Rates of oxidation were studied as a function of oxygen concentration and permeability characteristics of materials used to package the bars determined. A mathematical model for prediction of storage life of the product was formulated using the kinetic data for shrimp oxidation and the permeability data. An iteration procedure utilizing a high-speed computer was used to solve the pertinent equations and to predict storage life. Predictions were compared with results of actual storage tests; those based upon pigment loss were better than those based upon changes in flavor score.     

CHANGES IN QUALITY OF DEHYDRATED KIBBLED ONIONS DURING STORAGE

SUMMARY— Dehydrated kibbled onions. of the Egyptian variety, containing 4-5% moisture, were stored under different conditions and their keeping quality as influenced by storage variables determined. 3 packaging materials, namely cans, polyethylene and Saran pouches were used. Samples were stored at temperatures of 15, 25 and 35°C at 44% relative humidity for 39 wk. Temperature of storage was found to have the largest effect on product quality. The can package was found to be superior to the flexible pouches; however, Saran pouches could be used under certain conditions. Moisture content increased significantly in polyethylene pouches at all temperatures, but in Saran pouches only at 25° C Absorbance of onion extracts, as measure of browning, increased significantly with storage temperature and to a smaller extent due to packaging materials. Products in polyethylene deteriorated most, while the difference between Saran- and can-packed products was small. A similar trend in results was found in tristimulus color determinations. All products stored at 15° C and those in cans at 25°C were found to be of good organoleptic quality. The pyruvic acid development potential could not be used as a sensitive indicator for determination of product quality.     

STORAGE STABILITY OF DRIED ONION

The effect of predrying treatment and conditions of storage on color stability of dried onion was investigated. The variety of onion had little effect on color stability, but storage time prior to drying affected the color of the dried onion. Steeping of sliced onion in water or dipping in starch solution lessened browning and allowed for longer storage. Ascorbic acid in the steeping solution yielded dried onion with a pink unacceptable color. Osmotic dewatering imparted a yellow color to the onion, but improved the color stability of the dried product. Light was an important variable in the storage stability of dried onion.     

SENSORY EVALUATION OF FOOD FIRMNESS

How people test foods for firmness without eating them, was studied using 131 respondents and 9 different pairs of foods representing a wide range of firmness. The results were related to correctness of judgment and objective characterization by the Instron machine. Evidence was obtained that the kind of sensory firmness test employed depends on the firmness of the food. Viscosity/ consistency, deformation, puncture, and flexure were used as the degree of ‘firmness’ increased from a low (whipped toppings) to a very high (carrots) level.     

STORAGE STABILITY OF MILKFAT GLOBULE MEMBRANE

To investigate changes in structure and function of milk fat globule membrane (MFGM) components due to oxidation of membrane lipids, freeze-dried MFGM were stored under controlled temperature and relative humidity (RH) conditions. It was found that while membranes underwent extensive lipid oxidation when stored under air, fluorescent compounds were formed. These compounds exhibited fluorescence with excitation maxima at 350 nm and emission maxima at 440 nm; which were similar to those of the fluorescent substances derived from the reaction of oxidized fatty acids and primary amines. Formation of high molecular weight proteins was detected by SDS-PAGE in samples stored under air, but not in samples stored under nitrogen and was also affected by time and relative humidity. Activity of xanthine-oxidase, an important prooxidative agent, was greatly influenced by temperature and complete inactivation was observed when MFGM's were stored at 37°C, 50% RH for 1 day.     

EFFECT OF STORAGE ON NUTRITIVE VALUE OF FOOD1

With few exceptions, nutrient levels and/or their bioavailability are reduced in foods following harvest, slaughter, or collection. Rate of these losses is usually attenuated by reducing temperature of storage. Initial heat processing to the point of enzyme inactivation, or to the point of microbial sterilization, “stabilizes” the food so that it does not “spoil” but at the same time causes a greater initial reduction in certain nutrients, and a more gradual reduction with extended storage. Initial heat processing and mechanical treatments may also release nutrients so that they become more available, but once released, they are also subject to losses unless stored at low temperatures. Ascorbic acid is undoubtedly the most sensitive to loss and changes to a less active form as the result of time and temperature in storage. In many instances changes in ascorbic acid reflect general changes in quality. Thiamine is the other vitamin which is frequently affected adversely by time and temperature of storage. The A vitamins appear to be lost readily in leafy vegetables, but relatively unchanged in other foods. There is little effect on mineral content of foods, but bioavailability, particularly of iron may be influenced during prolonged storage. Substantial losses in carbohydrates may be encountered as a result of respiratory activity in extended storage at relatively high temperatures. Protein content is rarely affected, but protein availability is readily reduced even in low moisture foods unless they are protected from oxygen and stored at low temperatures. These anticipated changes in nutritive value are of particular significance in nutrient labeling, and must be taken into account when preparing nutrient labels.