The use of carbon dioxide in the processing and packaging of milk and dairy products: A review

The upswing in consumer demand for fresh and high quality preservative‐free foods has led to the development of modified atmosphere packaging (MAP). Increasingly, MAP is being used with high carbon dioxide (CO₂) concentration as well as CO₂/N₂ gas mixes. Modified atmosphere packaging or ‘gas flushing’ as it is also known is an increasingly popular technique used to extend the shelf life (both quality and safety) of a number of dairy products. Carbon dioxide is an active constituent of MAP, naturally present in freshly drawn raw milk. Addition of CO₂ to raw milk or flushing the package headspace has proved to be a simple and cost‐effective method, depending upon the initial microbiological quality of the food product. Carbon dioxide addition through MAP or direct injection as an economically affordable shelf life extension strategy is used commercially worldwide for some dairy products. The development of food packaging machines with integrated gas flushing capabilities and the supply of ‘food grade’ gases allow dairy foods manufacturers to enhance the quality of their products. This review presents a broad spectrum of current research and the current trends with respect to CO₂ as a natural microbial hurdle with special focus on its precise mechanism and its role in quality improvement of dairy products.     

Prediction of Thermal Conductivity of Fruit Juices by a Thermal Resistance Model

A model for prediction of thermal conductivity of fruit juices was developed. The model was based on the concept of thermal resistances in parallel and compared with other models and experimental values. Effect of temperature and solid concentration on thermal conductivity was discussed. Extension of the model to predict thermal conductivity of fruit juices below the freezing temperature was briefly discussed. The model gave error of less than 10% from the experimental values for juices for which such values were available.     

Competitive Adsorption Between Sodium Caseinate and Oil-Soluble and Water-Soluble Surfactants in Oil-in-Water Emulsions

Competitive adsorption between sodium caseinate and either a water-soluble surfactant, Tween 60 (polyoxyethylene sorbitan monostearate—PSM) or an oil-soluble surfactant, Span 60 (sorbitan monostearate—SM) was studied in oil-in-water emulsions. Surfactants were present during homogenization. Surface concentration of protein in freshly prepared emulsions decreased as concentration of PSM or SM increased. However, only partial displacement of protein was observed with either surfactant. The reduction in protein surface concentration was greater in the presence of PSM. Interfacial protein composition was independent of surfactant type. In the absence of surfactant, preferential adsorption of β-casein occured in emulsions containing ≤1.0 wt % protein. On addition of surfactant preference for β-casein at the interface was reduced.     

A Kinetic Approach to Food Quality Prediction Using Full-History Time-Temperature Indicators

A mathematical model based on the theory of chemical kinetics was derived to predict food quality change from the response of a full-history time-temperature indicator. A first-order kinetic reaction (n = 1) was used to describe both indicator response and changes in food quality. A storage investigation of mature green tomatoes showed that the quality prediction model satisfactorily predicted changes in tomato firmness induced by variable temperature storage. Tomato firmness as predicted from the response of a LifeLines model 57 time-temperature indicator was not significantly different from the observed changes (F = 1.99, p = 0.18) for 28 days of storage. The mathematical derivation was extended to develop a quality-based interpretation of the shelf life of perishable foods.     

MECHANICAL PROPERTIES OF AN IMMERSION FRIED POTATO STARCH-GLUTEN GEL DURING POSTFRYING PERIOD

Moisture profiles in fried samples of potato starch with different gluten contents were determined during postfrying storage. Over time, moisture migrated from the core to the crust of the sample, and the moisture content of the crust region increased. The addition of gluten caused a significant increase in oil uptake in the crust. The initial hardness of the crust significantly decreased as the gluten content increased to 10 and 30%, during the first 30 min of storage. With longer storage time (> 240 min), the crust hardness tended to increase, due to an increase in firmness of the starch sample. This behavior was less pronounced for samples with 10 and 30% gluten. The range of linear viscoelastic behavior (up to 14% strain) was determined from the initial linear zone of the stress-strain curves. Stress relaxation tests were performed in the linear and nonlinear viscoelastic regions, with a strain level of 5% and 40%, respectively. According to stress relaxation curves, samples became less elastic with the addition of gluten and more elastic with the time of storage.     

STUDIES ON OCCURRENCE AND CHARACTERIZATION OF CLOSTRIDIUM PERFRINGENS FROM SELECT MEATS

A study was undertaken to assess the prevalence of Clostridium perfringens in meat and to characterize the isolates obtained in the study for virulence factors. A total of 211 meat samples of different animals (70 each of buffalo and goat and 71 of poultry) were screened and the highest occurrence of C. perfringens was observed in goat (91.4%) followed by poultry (70.4%) and buffalo (65.7%). Among the 116 isolates (buffalo‐32, goat‐37 and poultry‐45) of C. perfringens screened for the presence of enterotoxin gene by PCR, 9.3, 32.4 and 15.5% isolates of buffalo, goat and poultry, respectively, were found to possess enterotoxin gene. Screening of 15 enterotoxin gene possessing isolates for verocytotoxicity revealed that 12 isolates exhibited cytopathic effect while 3 isolates did not show any cytopathic effect in spite of the presence of enterotoxin gene. A total of 115 C. perfringens isolates were screened for other virulence markers, i.e., lecithinase and hemolysin. The results revealed that the majority of the isolates expressed these activities. Antibiogram studies of C. perfringens isolates using 16 antibiotics displayed multidrug resistance. The isolates showed resistance to streptomycin, ceftazidime, colistin sulfate, cephalothin, ampicillin and gentamicin. Whereas 100% sensitivity to ciprofloxacin, ofloxacin and nitrofurantoin was seen, moderate sensitivity was observed with tetracycline and sulfatriad.     

QUALITY OF MEAT PRODUCTS DURING REFRIGERATED AND ULTRA-CHILLED STORAGE

Standard domestic refrigerators store food between 1 and 5C (33.8–41F). A manufacturer recently developed a refrigerator capable of storing food in the “ultra‐chilled region” (?3 to ?7C) and claimed that storage of fresh meat in this region better maintains quality. To understand quality in terms of chemical reaction rates, microbial growth and texture and flavor changes, three common consumer meat products – steak, ground beef patty and salmon – were stored for a selected period of time, as determined by microbial testing, in five refrigerator models with different environmental conditions (constant temperature and temperature fluctuation). At the end of the storage period, consumer panelists assessed the quality of the cooked samples by ranking them according to preference. In addition, instruments were used to measure the color and shear cutting force (for steak only) of each sample. Results from the consumer Ranking R‐Index Test indicate that panelists preferred samples stored under or near ultra‐chilled conditions rather than samples stored under standard refrigerated conditions. The ultra‐chilled samples not only had higher panelist rankings and more favorable comments, but also had lower microbial aerobic plate counts. The instrument readings, however, highly varied and did not correlate well with sensory data.     

PALATABILITY AND VISUAL CHARACTERISTICS OF HAMS AND LOIN CHOPS FROM SWINE TREATED WITH RACTOPAMINE HYDROCHLORIDE

This study was designed to evaluate the visual and palatability characteristics of boneless cured hams and fresh loin chops from pigs fed diets containing 0, 5, 10 or 20 ppm of the phenethanolamine, ractopamine hydrochloride (RAC). Sixty pigs were blocked by starting weight and randomly assigned to pens (four pigs/pen) within each of three blocks. Treatments were then randomly assigned to pens (six pens of the 0–ppm level and three pens each for the 5, 10 and 20 ppm RAC levels). Animals were slaughtered by weight block after approximately 48 days on trial. Fresh pork hams and loin sections (10–14th rib) were removed from the right side of the carcasses for subsequent analysis. Boneless hams were manufactured using commercial curing procedures. RAC had no effect (P > 0.05) on visual or palatability attributes of ham slices or boneless loin chops. Moisture content of the longissimus muscle from RAC treatments was lower (P < 0.05) than controls; however, this difference was small. These results indicate that RAC had no affect on the visual or palatability characteristics of boneless cured and smoked hams or fresh boneless pork loin chops.     

Study of Bacterial Samples Using Laser Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy （LIBS） technique has been applied to inves- tigate two different types of bacteria, Escherichia coli （B1） and Micrococcus luteus （B2） deposited on glass slides using Spectrolaser 7000. LIBS spectra were analyzed using spectrolaser software. LIBS spectrum of glass substrate was compared with bacteria spectra. Ca, Mg, Na, K, P, S, C1, Fe, A1, Mn, Cu, C, H and CN-band appeared in bacterial samples in air. Two carbon lines at 193.02 nm, 247.88 nm and one hydrogen line at 656.28 nm with intensity ratios of 1.9, 1.83 and 1.53 appeared in bacterial samples B1 and B2 respectively. Carbon and hydrogen are the important components of the bio-samples like bacteria and other cancer cells. Investigation on LIBS spectra of the samples in He and Ar atmospheres is also presented. Ni lines appeared only in B2 sample in Ar atmosphere. From the present experimental results we are able to show that LIBS technique has a potential in the identification and discrimination of different types of bacteria.