EFFECT OF OXYGEN-ENRICHED ATMOSPHERES ON STORAGE QUALITY OF PACKAGED FRESH MEAT

SUMMARY —The extension of fresh meat shelf-life is important from both practical and theoretical points of view. Color is usually used as a measure of fresh meat quality during storage. Beef top-round slices were prepared using sanitary precautions. Meat slices were enclosed in a thermally sealed semi-rigid polyvinyl chloride tray system of special design. Face-to-face meat samples were used to compare the effects of high oxygen with normal air atmospheres. One package from each pair was evacuated and the atmosphere readjusted to approximately 90% oxygen through a septum. Packages were kept at 4 ± 0.5°C and gas chromatographic readings for CO₂, O₂ and N₂ were conducted daily. Spectrophotometric and bacteriological evaluations were made on selected pack ages during storage to determine pigment oxidation and microbial growth. Three experiments each containing six to eight pairs of samples were conducted. The generation of CO₂ was observed in two periods–the first immediately after packaging and lasting for 1–2 days, after which the CO₂ level remained approximately stable up to 8—9 days, when it again started to increase in correspondence with increased bacterial growth. There was more CO₂ produced than O₂ utilized in the stored samples. In the first stage, samples stored in oxygen-enriched atmospheres had higher O₂ uptake than samples stored in air. Microbial growth was similar in both atmospheres. Under conditions of this study, head space enrichment to about 90% oxygen prolonged acceptable meat color when compared with samples stored in an air atmosphere.     

MICROBIAL GROWTH IN PACKAGED FRESH ASPARAGUS

The effects of storage temperature and time on the microflora of fresh, vacuum packaged, and modified atmospheres packaged asparagus (Asparagus officinalis) were analyzed. Total aerobic mesophilic, psychrophilic, lactic acid bacteria, Enterobacteriaceae, and yeast and molds were determined as a function of time. The effect of washing on the original microflora of the asparagus and the growth of the different microbial groups during the storage time were checked. From day 8, a progressive increase in the mesophile and psychrophile counts in both types of packaging was observed. At the end of the experiment (day 21), the mesophile and psychrophile counts were all 10⁷ CFU/g, for both types of packaging. In the vacuum packaging, the final enterobacteria counts (2.5 × 10² CFU/g) and yeast and molds (10 CFU/g) were lower than in the polyethylene bag packaged asparagus, which showed enterobacteria counts of 7.3 × 10⁴ CFU/g) and yeast and mold counts of 2.3 × 10⁴ CFU/g. The non-packaged asparagus showed low counts from the fourth day due to their heavy dehydration caused by the low relative humidity in the storage chamber.     

CHANGES IN THE MICROFLORA OF PACKAGED FRESH BROCCOLI

Changes in the microflora of fresh broccoli shrink-wrapped in film, sealed in gas-flushed film pouches, or stored on ice in cardboard crates and held at 1°C were analyzed. Growth trends for total aerobes, psychrotrophs, yeast/molds, members of Enterobacteriaceae, and lactic acid bacteria did not differ significantly between the packaging treatments (p ≤ 0.05). However, populations of total aerobes in unpackaged broccoli in its final week of storage (week 6) were significantly greater than that of packaged broccoli at week 6. Samples packaged in film remained higher in quality 2 to 3 weeks longer than control samples. Yellowing was the most obvious defect.     

A MACHINE FOR MEASURING YIELD POINT IN RAW MEAT

A simple machine is described for measuring yield point in strips of raw muscle, by registering maximum tension generated at a low rate of extension. Values are not highly dependent on the rate or degree of extension. The method has been used to measure rate of ageing at 15°C and 2°C, with parallel measurements of shear force in the cooked muscle. The machine provides a sensitive tool, complementary to the tenderometer, and particularly suited to studies on ageing.     

THE BIOCHEMICAL BASIS FOR DISCOLORATION IN FRESH MEAT: A REVIEW

The color of fresh meat is an extremely important characteristic influencing the consumer's purchase decision. The stability of pigments in meat is highly variable and is governed by a variety of factors. The effects of exogenous factors (i.e., storage and display conditions) have been well researched. The control of these variables currently offers the best means for maximizing meat color stability. Biochemical factors which are inherent to the meat itself have received far less research attention and an understanding of these presents the greatest potential for prolonging color stability in fresh meat.     

CHANGES IN THE MICROFLORA OF PACKAGED FRESH TOMATOES

Fresh tomatoes were shrink-wrapped in film, sealed in gas-flushed film pouches, or stored in cardboard packing crates. All samples were stored at 13°C, and changes in populations of total aerobes, psychrotrophs, yeasts and molds, members of Enterobacteriaceae, and lactic acid bacteria followed. Shrink-wrapping and gas-packaging increased aerobic counts over no packaging, and selected for yeasts and molds. Shrink-wrapping additionally selected for lactic acid bacteria. The greatest number of psychrotrophs but the least number of yeasts and molds developed in unpackaged tomatoes. Shrink-wrapped and gas-packaged tomatoes remained unspoiled at least 6 weeks whereas controls spoiled in 4 weeks.     

INSTRUMENT FOR MEASURING BIND STRENGTH OF RESTRUCTURED AND EMULSION-TYPE MEAT PRODUCTS1

A sensitive and inexpensive penetrometer is described, consisting of a mounted rod and polished steel ball that may be advanced downward at variable speed through meat slices mounted on a plexiglass cylinder. The slice + mounting cylinder was placed on a top-loading balance, tared to zero, and centered under the penetrometer rod. Bind strength was measured as the peak force (g) required for the steel ball advancing at 2.0 cm/min to penetrate the meat slice. Data points (grams force versus time) were collected and plotted using an IBM-compatible personal computer and printer. Since the balance collected gram values continuously, a QuickBasic program was developed, allowing the user to specify the time interval (1,2,5 s, etc.) between recorded values. Bind strength of turkey rolls was increased by finely chopping the emulsion (vs. coarsely-ground samples), and by inclusion of 3% nonfat dry milk. Whey protein concentrate (3%) increased bind strength of finely chopped, but not coarsely ground rolls.     

CO/CO2/N2三种气体协同对冷却猪肉保鲜及护色效果的研究

为了延长冷却肉的货架期,采用添加一定浓度CO的方法进行护色处理,CO能与肌红蛋白(Mb)强烈结合形成碳氧肌红蛋白(MbCO).使肉在货架期内呈现樱桃红色.研究在混合气体中添加低浓度的CO气调包装对冷却猪肉的保鲜效果,测定贮存过程中的微生物、理化和感官指标(特别是色泽)的变化,确定适合的冷却猪肉气调包装混合气体比例为1%CO/50?2/49%N2,不但延长了货架期,而且使冷却肉在整个货架期内呈现诱人的亮红色.     

PHOTO SENSITIVITY OF FRESH MEAT COLOR IN THE VISIBLE SPECTRUM

SUMMARY –The effect of specific wavelengths of visible light on fresh meat color was investigated. 2-in. diam cores of meat were aseptically prepared from top rounds (adductor muscle and semimembranosus muscle). Freshly oxygenated face-to-face cuts were used as the sample and control. The sample and control were packaged in mylar polyethylene pouches and cooled moist filtered air was circulated through the pouch for the duration of the experiment. Samples were exposed to the following wavelengths at an energy level of 0.5 mw/cm²: 420.0, 510.0, 550.0, 570.0, 590.0 and 632.8 nm. Experiments were conducted at 34°± 1°F and 41°± 1°F for 2 and 5 days of exposure. The controls were next to the sample but kept in darkness during the exposure period. There was no temperature differential between the sample and control. Oxidized heme pigment content was determined by reflectance spectrophotometry. No wavelength enhanced the formation of oxidized heme pigment more than any other, however illuminated samples contained an average of 5.5% more oxidized heme pigment than did the controls. Oxidized heme pigment content increased with lengthened storage time and increased temperature. The increase in oxidized heme pigment content as a result of illumination may be due to a photochemical activation of a compound such as riboflavin which then may react with oxygenated heme pigments to form oxidized heme pigments.     

REFINEMENTS OF THE CASEIN TURBIDITY METHOD FOR MEASURING PROTEASES IN BEER

The casein turbidity method for determining papain has been modified to allow it to be used for both normal and strong beers. Problems of instant casein coagulation which occur when the original reagents are mixed with strong beers were due to inadequate control of pH, and not to high alcohol levels. Methods are given for preparing convenient substrate and activator solutions that are stable for at least 8 days at 4°C. By carrying out estimations at 60°, rather than 50° as originally proposed, incubation times are roughly halved. It is shown that weak activators, like potassium metabisulphite, can reduce enzyme activities when added to a reaction mixture which also contains cysteine. The mixing sequence of beer, activator solution and substrate solution, as well as buffer strengths, influence the observed activities of papain. Further changes which might improve the method further have been proposed.     

BOTULINAL TOXIN PRODUCTION IN VACUUM AND CARBON DIOXIDE PACKAGED MEAT DURING CHILLED STORAGE AT 2 AND 4C

This study was undertaken to determine if carbon dioxide packaging of meat afforded a food safety advantage over vacuum packaging with respect to botulinal toxin production during chilled storage. A cocktail of washed spores from five toxigenic clostridial strains – four reference Clostridium botulinum strains [types A, B (2 strains) and E] and a C. butyricum type E strain – was inoculated onto lamb chumps. Of these strains, two were psychrotolerant. The inoculated chumps were individually carbon dioxide packaged and duplicate packs were placed into storage at 10, 8, 6, 4 and 2C. All storage regimens included a weekly defrost cycle when meat surface temperatures increased by up to 6 to 7C during a 2 to 2.5 h period. After 84 days storage, packs were assessed for the presence of botulinal toxin using the mouse bioassay procedure. All packs contained botulinal toxin. To compare toxin production in vacuum and carbon dioxide packs at chill temperatures, the challenge trials were repeated for 4 and 2C storage. Packs were examined at regular intervals for toxin presence. Both pack types contained toxin after 21 and 48 days storage at 4 and 2C, respectively. In the unlikely, but not impossible, event that raw meat would be contaminated with psychrotolerant toxincapable clostridial spores, product safety, with respect to botulinal toxin presence after prolonged chilled storage, requires storage temperatures to be maintained below 2C for both vacuum and carbon dioxide packaged product.     

THE UTILIZATION OF MODIFIED GAS ATMOSPHERE PACKAGING FOR FRESH MEAT: A REVIEW

Distribution and packaging methods that are used for fresh meats have changed drastically over the past decade from primarily the shipment of carcasses to vacuum packaged primal cuts. Research efforts are now being directed at the replacement of vacuum packaging with modified gas atmospheres which may be more cost efficient and reduce trim losses. This paper reviews some of the more current research which has been conducted in modified gas atmosphere packaging.     

A METHOD FOR MEASURING THERMAL TIME DISTRIBUTIONS IN CONTINUOUS FLOW HEAT EXCHANGERS

This study deals with the distribution of heat treatment of liquids which flow through heat exchangers. the distribution is induced by the combined effect of velocity and temperature gradients and is referred to as the thermal time distribution (TTD).
A tracer technique based on the acid hydrolysis of dextran was developed for assessing the TTD. the change in the shape of the molecular weight distribution (MWD) of the polymer during the course of the reaction was found to be related to the TTD exposure of the fluid and the shape of the MWD could be described by means of statistical moments.
A computer-based model for simulating the TTD in a tube heat exchanger, in turbulent flow, was developed together with a model for simulating the effect of the TTD on the change in the MWD during dextran hydrolysis. the simulation model gave results that were in qualitative agreement with the experiments.     

COMPARISON OF 2-THIOBARBITURIC ACID REACTIVE SUBSTANCES DETERMINATION METHODS IN VARIOUS TYPES OF FROZEN, FRESH MEAT

Triplicate batches of chicken breast (CB), chicken thigh (CT), fresh ground beef (GB), ground beef patties frozen 2 years (BP), veal (V), pork roast (PR), ground pork frozen 1 year (GP) and lamb (L) were homogenized and subjected to each of five 2-thiobarbituric acid reactive substances determination methods (n = 3 TBARS determinations/sample/method/replicate). Distillation methods resulted in higher (p < 0.05) TBARS values than extraction methods for all types of samples. TBARS ranges were CB=0.21–0.55; CT=0.21–0.40; GB=0.26–0.89; BP=1.14–4.00; V=0.18–0.82; PR=0.67–2.09; GP=1.17–4.01; and L=0.58–2.18. Distillation methods in which antioxidant was added did not consistently produce lower TBARS than distillation without antioxidant. Distillation methods produced TBARS approximately 2 times those produced by extraction methods in less oxidized samples (CB, CT, GB, V); distillation methods produced TBARS 2.75 times those produced by extraction methods in more oxidized samples (BP, PR, GP). Recoveries were quite different (ranging from about 65% to 95%) for the various methods indicating the need to run both standard curves and recovery rather than using published conversion factors in TBARS calculations.     

对聚酯切片中羧基含量测定方法的改进

本文通过实验证实：以苯酚－氯仿混合溶剂（体积比为３：２）溶解切片，对提高测定羧基含量的准确度是有利的，从而对原方法进行改进。     

对测量水中SiO_2方法的改进

本文探讨用普通试剂替代进口色剂检测水中ＳｉＯ２的方法．