INHIBITION OF SPOILAGE AND PATHOGENIC BACTERIA ASSOCIATED WITH FOODS BY COMBINATIONS OF ANTIMICROBIAL AGENTS

The antibacterial activity of combinations of lysozyme, monolaurin (ML), triglycerol 1,2 laurate (TGL) and butylated hydroxyanizole (BHA) against 7 Gram-positive and 8 Gram-negative bacteria was studied at different pH, NaCl and EDTA concentrations by the spiral gradient end point test. The inhibitory effect of lysozyme in combination with ML was slightly greater for Gram-positive than for Gram-negative bacteria, but their combined effect was not markedly more inhibitory than ML alone. Lysozyme and TGL together were only inhibitory at low pH and high NaCl concentrations in the presence of EDTA. There was an increase in inhibition when lysozyme and BHA were combined. For Gram-positive bacteria, inhibition by ML and BHA together was more marked than when either was present singly. However, ML decreased the antibacterial activity of BHA against Gram-negative bacteria. Similarly, TGL was antagonistic to BHA action against both Gram-positive and Gram-negative bacteria. In general, the inhibition produced by all combinations was greater as the pH decreased and the NaCl concentration increased, especially in the presence of EDTA .     

MECHANISMS OF FRACTURE IN FOODS

Most foods have solid-like properties and therefore must be size reduced in the mouth before swallowing. In this paper we will examine the physics of the fracture processes involved in breaking different food types. These range widely from brittle fracture in dry cereal foods, nuts, and fresh vegetables, to the complex defibrillation and tensile failure in cooked meats. We will examine how the differences in fracture and failure processes correlate with our perception of quality in various food types. This allows deduction of an overall model for the mastication process and how consumers may develop preferences for particular foods. The real stresses and strains exerted in the mouth are difficult to identify in local, spacial detail. Recent work is beginning to define how mouth motion controls the fracture process, and the impact of saliva on the mechanism of swallowing.     

ROLE OF BACTERIAL PROTEOLYSIS IN THE SPOILAGE OF IRRADIATED FLESH FOODS

Microorganisms (Aeromonas hydrophila, Bacillus megaterium, Pseudomonas marinoglutinosa and Salmonella typhimurium) proliferated equally well when incubated in unirradiated and irradiated fish myofibrillar protein fractions. However, formation of Total Volatile Bases was found to be 50–60% less in the irradiated myofibrillar protein fraction. Proteolysis measured in terms of tyrosine release also registered 50% less in irradiated flesh foods as compared to unirradiated samples under identical conditions. Bacterial protease levels were also evaluated after growth in both control and irradiated fish proteins using hemoglobin as substrate which revealed that there is considerable reduction in protease secretion when the bacterium proliferated in irradiated fish proteins. These results suggest that appreciable delay in the spoilage of irradiated flesh foods could be attributed to low bacterial proteolysis.     

EFFECTS OF LONG-TERM STORAGE OF FOODS ON QUALITY OF PROCESSED FOODS II.

The effects of long-term storage at 4.4, 21.1, and 37.8°C on physicochemical characteristics, nutritional and organoleptic qualities of freeze-dehydrated ration items from Packet Long Range Patrol were studied. The items included beef hash, beef stew, chicken stew, spaghetti with meat sauce, chili con carne with beans, chicken and rice, pork with escalloped potato, and beef and rice. The freeze-dehy drated foods were stable in quality during storage at 4.4, 21.1, and 37.8°C. After 44 months of storage all freeze-dehy drated ration items were in acceptable condition.     

油炸食品中两种酚类抗氧剂的反相高效液相色谱法测定

采用反相高效液相色谱法测定油炸食品中叔丁基对苯二酚（TBHQ）、抗氧剂2246的含量.正己烷饱和的乙腈做提取剂,以甲醇为流动相,227 nm波长检测.在0.11mg/L～56.00mg/L范围内,线性相关系数均为0.999 9,检出限分别为：0.22 mg/L,0.11mg/L,相对标准偏差在0.19%～2.87%之间,平均回收率均在85.0%以上.3种油炸方便面、薯条、豌豆脆样品中未检出抗氧剂2246,均有叔丁基对苯二酚检出.     

COMPUTER SIMULATION OF VITAMIN DEGRADATION IN A DRY MODEL FOOD SYSTEM DURING STORAGE1

During storage of dry foods, oxidative mechanisms can result in nutrient degradation. Accurate prediction of the vitamin content for dry foods during storage is essential to provide the processor with the assurance of meeting label claims. Since appropriate shelf-life tests for measurement of vitamin degradation represents an alternative worth considering. A mathematical model of the relationship between the rate constant of ascorbic acid oxidation and water activity was established. Computer simulation to predict product moisture content and ascorbic acid degradation in a dry model food product was developed by considering the simultaneous influence of water activity and temperature on rate constants which change with storage time due to varying storage environments. The computer simulation predicts product moisture content and vitamin degradation in good agreement with the experimental data. The simulation will account for the influence of storage temperature and relative humidity as well as characteristics of the food product and package material.     

EFFECTS OF LONG-TERM STORAGE ON QUALITY OF PROCESSED FOODS

Experiments were conducted on the effects of long-term storage at 4.4, 21.1, and 37.8°C temperatures on nutritional quality, physicochemical characteristics and organoleptic quality of 8 food packets (ready to eat individual ration items processed in flexible retortable pouches) of ham and chicken loaf, beef steak, beef stew, frankfurters, fruit cake, pineapple slices, cheese spread, and chocolate brownies. At 37.8°C storage life of cheese spread, pineapple slices, beef stew, chocolate brownies and fruit cake was 12, 12, 30, 30 and 30 months respectively. Ham and chicken loaf, beef steak, and frankfurters were acceptable after 37.8°C storage for 54 months, but frankfurters were near the borderline of rejection. The browning is usually associated with the high temperature storage of high sugar foods. Meat products except beef stew are apparently more stable than others at high temperature storage. The high temperature storage resulted in drastic loss of thiamin and ascorbic acid, significant loss of riboflavin and niacin, and discoloration and rancidity. Despite the losses of quality observed in all food packets stored at 21.1°C for 54 months, they were acceptable. Storage at 4.4°C for 54 months had very little effect on quality of the food packets and were highly acceptable.     

SPOILAGE OF ANCHOVY-STUFFED OLIVES BY HETEROFERMENTATIVE LACTOBACILLI1

An unusual type of spoilage was encountered in canned green olives stuffed with anchovies. The spoilage was characterized by a gradual decrease in acidity of the olive brine from about pH 4.3 to 5.25 and a swelling of the cans caused by CO². Spoilage of the product was caused by decomposition of the anchovies by proteolytic enzyme action, with subsequent decarboxylation and deamination of amino acids from the anchovies by heterofermentative lactobacilli. This type of spoilage, known as “protein swells”, occurs with canned fish marinades but, to our knowledge, does not occur with other acidified canned foods.     

COMPUTER SIMULATION of MICROBIAL GROWTH DURING FREEZING and FROZEN FOOD STORAGE

A computer simulation model was developed to predict the time for temperature equilibration as well as microbial growth within a food product during freezing and the equilibration to frozen storage conditions. Theoretical results indicate that freezing medium temperature, surface heat transfer coefficient and product size influence the equilibration time significantly. Storage conditions influenced the equilibration time during storage and significantly influenced the growth of microorganisms. Microbial growth is a function of the freezing time. Slow freezing of a food product from a high initial temperature and stored at a relatively high temperature can provide conditions for microbial growth as compared to very rapid freezing processes. the model is a useful tool for approximate indications of effects of freezing conditions on microbial growth within a food product.     

EFFECT OF STORAGE ON THE RHEOLOGICAL BEHAVIOUR OF BABY FOODS

The effect of storage temperature on rheological behaviour of four varieties of baby foods was studied. After 24-month storage at 15C and 25C, the constant A in Weltman model increased significantly for the vegetables, meat and fish samples, and decreased significantly for the fruit samples. After 24-month storage at 5C and 15C there were no significant changes in flow behavior index, consistency index and yield stress of the Herschel-Bulkley model for the vegetables, meat, fish and fruit samples. Increase in storage temperature decreased the consistency index and yield stress of the fruit samples.