A COMPARISON OF THE EFFECTS OF TEMPERATURE,ENZYME SOURCE,AND SEQUENCE OF DIGESTION ON NEUTRAL DETERGENT FIBER1

ABSTRACT A number of methods for determining dietary fiber have been suggested. Thus, ten modifications of the neutral detergent fiber (NDF) procedure were compared using spinach, bread, and parsnips. Use of Bacillus subtilis alpha amylase resulted in lower (p < .01) NDF values than did porcine pancreatic amylase. Amylase obtained from B. subtilis may contain other enzymes such as hemicellulase and cellulase in small amounts. These enzymes would be undesirable since they may remove some of the fiber fraction, hence the reported NDF would be lower. Temperature of incubation, 21°C or 37°C, did not significantly affect fiber values. Samples predigested with amylase had higher (p < .01) fiber values in a high starch food than samples in which amylase incubation occurred after detergent digestion. NDF values may have been higher because starch was less available for enzymatic hydrolysis before the detergent digestion. When amylase was added directly to the detergent solution after refluxing, NDF was not significantly different (p < .05) from that quantified by the official AACC method or most of the other treatments. Implications of these findings are discussed with respect to their significance in practical applications.     

STRUCTURE AND COLOR CHANGES DUE TO THERMAL TREATMENTS IN DESALTED COD

Cod (Gadus morhua) has a great importance in some European countries, either due to fish production and exportation volume or because of its high consumption. Desalted cod (3.94 ± 0.04% salt content and 73.49 ± 0.06% water content) has a limited shelf-life due to the microbial activity and the autolytic proteolysis affecting product texture. Thermal treatments can be used to preserve the cod, but these can cause changes in color, fish muscle tenderization through protein denaturation and collagen breakdown. In this research, steam blanching (5 min), water blanching (1 min) and microwave heating (5 W/g, 2 min) were applied to desalted cod. The effect of these treatments on color (CIEL*a*b* coordinates), mechanical properties (shear and TPA tests) and microstructure of cod were analyzed. Thermally treated cod were lighter, slightly yellowed and softer. From color data and microstructural observations, heat induced changes in cod were a little smaller than in microwave heated cod.     

PREDICTION OF NEUTRAL AND ACID DETERGENT FIBER CONTENT OF GREEN ASPARAGUS STORED UNDER REFRIGERATION AND MODIFIED ATMOSPHERE CONDITIONS BY NEAR-INFRARED REFLECTANCE SPECTROSCOPY

The influence of the cultivar, harvesting time and length of storage under refrigeration and modified atmosphere conditions on the fiber content of green asparagus, grown in Huétor‐Tájar, Granada, Spain, was studied. Neutral detergent (NDF) and acid detergent (ADF) fiber content evolution was measured after specified storage conditions. Near‐infrared (NIR) calibration equations were developed and validated for these chemical characteristics. NIR spectroscopy was accurate in predicting NDF and ADF, proving its potential as a QC analytical technique.     

COMPOSITIONAL CHANGES OF STRAWBERRY DUE TO DEHYDRATION, COLD STORAGE AND FREEZING–THAWING PROCESSES

Strawberry is an excellent source of food ingredients, although compositional changes might occur in improperly controlled processing, affecting product quality. In this article, changes in sugar composition (glucose, fructose and sucrose), citric acid, water and total soluble content, as induced by partial dehydration and freezing–thawing processes, were analyzed in strawberries (var. Camarosa). Osmotic dehydration (OD) with 65 °Brix sucrose solution, air drying (AD) at 45C, or combined treatments (OD–AD) were applied to reduce strawberries’ water content to 70–85%. Fresh and dehydrated samples were frozen (?40C, 24 h) and stored (?18C, 30 and 180 days). All samples processed by OD and OD–AD showed a significant sugar gain, and depending on the dehydration treatment, total or partial sucrose hydrolysis was observed. Dehydration treatments caused small losses of citric acid. During the freezing–thawing process, drip loss and enzymatic action also cause changes in sugar concentration, especially in OD‐treated samples.     

FOLATE LOSSES IN BEEF LIVER DUE TO COOKING AND FROZEN STORAGE1

Raw, broiled and fried beef liver samples were stored at ? 20°C in either vacuum or air-saturated packages. At periods of 0, 30, 60 and 90 days the folates were extracted in a 2% ascorbate solution and analyzed by the Lactobacillus casei microbiological assay. The folate content of raw beef liver was higher than previously reported which could be partly due to the ascorbate level used and the precautions taken during the extraction procedure. Broiling was shown to cause a 41% loss in folate activity while frying caused a 50% loss. Further losses in vitamin activity occurred during frozen storage, especially in nonvacuum packages, but stabilized after 30 days.     

热风式干燥对甘薯膳食纤维中抗性淀粉含量的影响

研究低温预风干后高温快速风干处理对甘薯膳食纤维中抗性淀粉含量的影响.低温预风干温度对甘薯膳食纤维中抗性淀粉含量的影响效果显著,而高温快速风干的温度和时间对抗性淀粉含量的影响效果不显著.低温预风干温度和抗性淀粉含量间的变化呈非线性关系.提高抗性淀粉含量的最佳工艺参数为:30℃低温预风干60h,再在60℃高温快速风干1 h,抗性淀粉含量可达11.26%.     

HEAT AND MASS TRANSFER FUNDAMENTALS APPLIED TO FOOD ENGINEERING1

There is a need for deeper qualitative and quantitative understanding of the heat and mass transfer mechanisms underlying various techniques for food production, processing, preservation and storage. This is important for the development of new food sources, for more economical and energy-efficient processing of food from existing sources, for better food quality and quality control, and for adherence to new regulations such as nutritional labeling and shelf-life dating. Several classes of food-processing problems are presented where advances can be made on the basis of improved understanding of heat and mass transfer mechanisms. These include cases of competing transport, cases where transport competes with kinetics of chemical or biochemical reactions, and cases where determination and understanding of the rate-determining factor are needed. Specific examples are drawn from drying processes, leaching and extraction, freezing, sterilization and enzyme deactivation, and artificial cultivation.     

QUANTITATIVE EXTRACTION OF NUCLEOTIDES FROM FROZEN MUSCLE SAMPLES OF ATLANTIC SALMON (SALMO SALAR) AND RAINBOW TROUT (ONCORHYNCHUS MYKISS): EFFECTS OF TIME TAKEN TO SAMPLE AND EXTRACTION METHOD

Muscle excised from the dorsal flank of Atlantic salmon and rainbow trout at death and up to 120 min postmortem (P.M.) was frozen in liquid M₂ and stored at ‐80C. Following acid extraction, on ice (method 1), or dry ice (method 2) samples were analyzed for cyclic nucleotides to determine the effect of time to sample, and extraction method. There was no pattern of change in nucleotide profile in either species up to 10 min P.M. At 120 min P.M., Atlantic salmon muscle extracted by method 2 had a higher IMP concentration than at any other time but there was no difference in adenylates. Ignoring time taken to sample, method 2 resulted in higher adenylate and lower IMP concentration than method 1. These results indicate that method 2 is most effective in obtaining realistic nucleotide concentrations from fish muscle because it maintains the tissue temperature below the critical freeze zone, (‐0.8 to ‐5C) prior to enzyme inactivation.     

TRANSLOCATION OF LEAD AND CADMIUM FROM FEED TO EDIBLE TISSUES OF SWINE1

In separate experiments, growing and/or finishing swine were fed a control diet and diets supplemented with various low levels of lead and cadmium, for periods up to 24 weeks. The levels of lead in different treatment groups were 2 (control), 6 and 21 parts per million (ppm), whereas those for cadmium were 0.2 (control), 2.4 and 10.1 ppm, respectively. Lead did not accumulate in skeletal muscles, but a dose-related increase was observed in bone, liver and kidney. In the case of cadmium, no increase was seen in skeletal muscles, bone or brain; the accumulation occurred primarily in kidney and liver. After cessation of lead supplementation the concentration of this metal declined in liver and kidney tissues. On the other hand, cadmium levels did not show any appreciable decline in kidney or liver during 12 weeks after an initial 12 weeks treatment. Lead and cadmium did not accumulate in edible muscles of swine, but the high concentrations of these metals that were recorded in liver and kidney would render these organs unfit for food purposes.     

TEXTURE AND COLOUR CHANGES IN MEAT DURING COOKING RELATED TO THERMAL DENATURATION OF MUSCLE PROTEINS1

Differential scanning calorimetry was used to select temperatures that diferentiated between thermal denaturation of the three major structural protein species in bovine muscle: myosin, collagen and actin. Samples of m. semimembranosus, m. semitendinosus and m. psoas major were heated to those different temperatures and evaluated sensorially. Three groups of sensory properties were needed to describe the main texture changes observed in the meat: 1. Firmness 2. Fiber cohesivity, bite-off force, residual bolus 3. Juiciness Firmness increased with thermal denaturation of the myofibrillar proteins (myosin; 40-60d?C and actin; 66-73d?C). Fiber cohesivity etc. decreased with collagen denaturation (56-62d?C). Reduction in juiciness was primarily associated with actin denaturation, while cooking loss increased over the whole temperature range. The property “total chewing work”, a composite of the first two texture groups mentioned, yielded like the judges' “total texture preference”, optimal texture in the 60-67d?C temperature region, implying denatured myosin and collagen but native actin. This meat was light pink-gray in colour, while the cooking juice released was dark red.     

THE FORMATION OF HEAT AND ENZYME INDUCED (PLASTEIN) GELS FROM PEPSIN-HYDROLYZED SOY PROTEIN ISOLATE1

A gel prepared by heating pepsin-hydrolyzed soy protein isolate (HSPI) had a higher turbidity and viscosity and less solubility than did its starting hydrolyzate. The gelling characteristics of the heated hydrolyzate were possibly due to hydrophobic interactions, as opposed to peptide bond reformation. The presence of pepsin was found to be necessary for gel formation at 37°C but could be successfully replaced by heat. Incubation of the concentrated HSPI at 95°C for 30 min was optimal for heat-induced gel formation. When soy protein isolate (SPI) was hydrolyzed with papain or bacterial protease, little gelation occurred (either by heat or enzyme induced gelation treatments).     

QUALITATIVE AND QUANTITATIVE CHANGES IN AEROBIC MICROFLORA FROM INTESTINAL CONTENTS OF SOUTH-BALTIC COD DURING STORAGE AT 1-2°C

SUMMARY— The bacterial flora of the intestinal content of cod (Gedus morrhua L) were investigated during a period of 1 year. The quantity of bacteria in recently caught fish was studied during the full period. the quality during only 6 months. 3 groups of fish from the same capture and fishing grounds were analyzed: fresh, and stored at 1–2°C for 5 and 10 days. It was seen that in general gram-positive bacterial flora dominated in recently caught fish, while after 5 and 10 days of storage gram-negative flora our numbered the former. In the intestinal contents of fresh fish the Vibrio species dominated, whereas at storage, Pseudomonas spp. became dominant. In fresh fish, the bacterial flora of stored fish amounted to 3.10% of the total initial quantity after 5 days of storage and 1.5% after 10 days. Also, the gram-positive flora decreased comparatively more rapidly than gram-negative flora. The authors believe that the temperature of 1–27°C may play a part in the decreasing number of flora, as well as some other factors not investigated in the present research.     

THE ELIMINATION OF ENTERIC BACTERIAL PATHOGENS FROM FOOD AND FEED OF ANIMAL ORIGIN BY GAMMA IRRADIATION WITH PARTICULAR REFERENCE TO SALMONELLA RADICIDATION1

Despite world-wide severe underreporting of food-transmitted disease of microbial origin, it is clear that the majority of such diseases is caused by enteropathogenic Enterobacteriaceae. Most of these are spread by foods of animal origin, consumed raw, or recontaminated subsequent to industrial or culinary heat processing. Radicidation with the help of gamma rays of carcasses or consumer size cuts presents a real solution to this problem. An ecologically based procedure for the estimation of the most probable effective dose for the elimination of enteric pathogens of bacterial origin from fresh meats, poultry and seafoods is described, special attention being paid to bacteriological analytical methodology found useful under conditions of practice. An additional advantage of this approach is, that it will allow easy assessment of lower doses, following reductions of initial enterobacterial loads, which should be attempted in parallel. It is demonstrated that most alleged counter-indications so far hampering the use of ionizing radiation in food processing have now been eliminated, allowing full advantage to be derived from radicidation as an essential contribution to the protection of the consumer against diseases of microbial aetiology spread by foods, similar to the mandatory pasteurization of milk.