EFFECT OF SUPERCRITICAL CARBON DIOXIDE ON MICROBIAL POPULATIONS IN SINGLE STRENGTH ORANGE JUICE1

The effect of supercritical carbon dioxide on aerobic total plate count (TPC) of fresh-squeezed and quick-frozen single strength orange juice from Valencia oranges was studied. Orange juice was treated with SC CO₂ at different temperatures (35° to 60°C) and pressures (8.3 to 33.1 MPa). SC CO₂ treatment at 35°C reduced the TPC by 2 log cycles after 1 h treatment at 33 MPa. At 45°C and 33 MPa 2 log cycles reduction required 45 mins, and 15 mins treatment was sufficient at 60°C. D values of temperature control samples decreased as temperature increased, while that of supercritically treated juice decreased as pressure increased. D values at 35, 45 and 60°C of the supercritically treated juice at 33.1 MPa were calculated as 28, 22.6 and 12.7 min, respectively. The calculated values of z were 180°C, 167°C and 72°C at 8.3 MPa, 20.7 MPa and 33.1 MPa, respectively.     

SHELF-LIFE STUDIES ON CARBON DIOXIDE PACKAGED FINFISt FROM THE GULF OF MEXICO

Modified atmosphere packaging using CO, was demonstrated to be effective in retarding the growth of microorganisms during storage of fresh fish from the Gulf of Mexico. At 4°C, there was at least a log difference in bacterial counts at 2, 4, and 6 days between fish stored in CO₂ as compared to control fish stored without CO₂. While the CO₂ atmosphere was shown to inhibit the growth of common spoilage types of bacteria such as gram-negative rods (Pseudomonas), stimulation of gram-positive bacteria such asLacto-bacillus was also demonstrated. Fish stored at 4°C for 2–8 days in a modified atmosphere containing CO₂ had lower TVN values than fish stored at the same temperature without CO₂. The results indicate that an extension of the shelf-life of fresh fish can be obtained by packaging and storing the fish in a CO₂ atmosphere.     

THE EFFECT OF TEMPERATURE ON MICROBIAL GROWTH IN ORANGE JUICE

Model functions were fitted (correlation coefficient [r], from 0.9258 to 0.9999) to the experimental microbial growth data in orange juice stored at 0, 4, 10 and 15C. The models predicted a microbial population of about 5.3 log cfu/mL after 15.5 days (0C) and that it would take 12.7 days to reach a microbial population of 6.0 log cfu/mL (4C). The first derivative of the microbial growth model function (10C) indicated a growth rate of about 0.5 log cfu/mL/day (day 1). The lag phase period at 0 and 4C was 9.5 and 2.8 days, respectively. The shelf life of orange juice (time to reach 6 log cfu/mL) determined experimentally was 17.9, 12.7 and 3 days and 10 h at 0, 4, 10 and 15C, respectively. Three shelf‐life predictive models were developed (r = from 0.9436 to 0.9999). The predictions of shelf life by the “algebraic” model were identical to those determined experimentally. This was also true for the relative rate of spoilage (RRS) model at 0 and 15C. On the other hand, the RRS model underestimated the shelf life of orange juice at 4 and 10C. The modified exponential model overestimated (at 0, 10 and 15C) and underestimated (at 4C) the shelf life of orange juice. An Arrhenius “split” plot with a break point at 7.6C depicted the effect of temperature on the rate of development of microbial generations. The absolute value of the slope of each portion, of the Arrhenius plot, above and below the break point was 12.5 and 4.5, respectively. The slope of the Arrhenius slope for the temperature range below the break point (7.6C) indicated a slower microbial growth.     

HEAT TREATMENT EFFECT ON TEXTURE CHANGES and THERMAL DENATURATION of PROTEINS IN BEEF MUSCLE

Meat tenderness is one of the most important quality criteria when evaluating results of cooking conditions. Changes in tenderness and weight losses of heat-treated meat (semitendinosus muscle) for different time-temperature combinations were analyzed; the relationship between protein denaturation and textural changes was studied.
Heat treatments of meat samples (1.5 cm in diameter, 2 cm long) were performed in a thermostatic bath in the 60–90C range. Maximum heating times were 180 min. Meat hardness was determined by Warner-Bratzler measurements using an Instron testing machine. Protein denaturation was followed by Differential Scanning Calorimetry (DSC) analyzing peaks for myosin (I and II), sarcoplasmatic proteins and collagen (II) and actin (III).
Between 60 and 64C, hardness decreased with cooking time until reaching the lowest asymptotic values. This was related to protein denaturation of peak I and II. Between 66 and 68C, hardness decreased at first but increased later due to actin denaturation; at the temperatures 81 and 90C no modifications were observed and hardness remained at its higher values.
The kinetic model proposed fit the experimental results satisfactorily. Activation energies of tenderizing and toughening processes are similar to those of protein denaturation of peak II and III. Weight losses due to cooking were also modelled increasing through the entire temperature range.     

EFFECT OF ORANGE JUICE COMPOSITION ON FLOW BEHAVIOUR OF SIX-FOLD CONCENTRATE

Abstract. The effect of the pulp content and the relative viscosity of the serum on the flow behaviour of a six-fold orange juice concentrate, as represented by the generalized Casson equation and the power law, was studied on samples prepared with a single factor varied at a time. These general flow equations, optimal in terms of multiple correlation coefficients, were established and confirmed on commercial samples. Both equations were successfully applied in predicting the flow behaviour of orange juice concentrates. The generalized Casson equation was found to be somewhat more accurate than the power law.     

EFFECT OF DIFFERENT PASTEURIZATION CONDITIONS ON ENZYME INACTIVATION OF ORANGE JUICE IN PILOT-SCALE EXPERIMENTS1

The orange juice pasteurization is associated with enzymatic degradation (primarily pectin-methylesterase) of soluble pectin. Time-temperature curves were established to study different pasteurization conditions on enzyme inactivation, for fresh single-strength orange juice from Florida, containing natural PME enzyme. The orange juice was heated in a DeLaval, model P5-VRB plate heat exchanger with heating and cooling sections, and a 0.0101 m³ volume holding tube. The temperature in the heat exchanger was controlled by means of a pneumatic proportional controller. The residence time in the holding tube of the heat exchanger was monitored by adjusting the flow rate of the positive feed pump. The calculated holding times to obtain 90% reduction of enzyme activity ranged from 33.27 s at 80C to 17.85 s at 90C.     

EFFECT of HEAT TREATMENT ON FIRMNESS of APPLES and APPLE SLICES

Effects of heat treatment on firmness of apples (Golden Delicious, McIntosh and Delicious) and apple slices were studied. Heat treatment (45C, for 1.75 h) of Golden Delicious and Delicious apples significantly increased their firmness, but no significant increase was observed for the McIntosh cultivar. After storage for 7 days at 2C, the treated apples were firmer than those stored at 10, 18, and 25C. Apple slices prepared from the heat treated apples were also firmer at 21 days storage than those prepared from nontreated apples: differences ranging from 12% for McIntosh to 48% for Delicious. This beneficial firming effect of heat treatment might have application in producing high quality minimally processed slices from Golden Delicious and Delicious apple cultivars.     

EFFECT OF HEAT TREATMENT ON THE QUALITY OF COOKED CARROTS

We investigated the effect of heat treatment on the quality of cooked carrots (texture, chemical, and sensory evaluation). Slices of three carrot varieties (Rubika, Kundulus, and Rothild) were cooked at 90–120°C for 2–70 min. Compressive failure stress and rupture work were a by a Zwick Universal Testing Machine. Textural softening could be expressed by an exponential equation of the type: S = A exp(-kt), where 6 = rupture stress, t = cooking time, and A and k are constants. Plotting k versus l/T (T = cooking temperature, °K) revealed an Arrhenius-type relationship with apparent activation energy of about 28, 27, and 22 Kcal/mole for Rubika, Rothild, and Kundulus varieties, respectively. Chemical analysis (dry matter and p-carotene) showed that the cooking process caused insignificant changes. Statistical analysis of the sensory assessments showed an overall significant preference for 3 mm slice thickness and 110°C cooking temperature.     

不同热处理条件对麦胚贮藏稳定性的影响研究

就干热空气、湿蒸汽、微波及湿蒸汽耦合微波的不同处理条件对麦胚贮藏稳定性的影响进行了研究.结果表明,湿蒸汽耦合微波处理方法可有效降低麦胚脂肪氧化酶的活力,即常压湿蒸汽处理5 min后再经320 W微波处理3min,其相对酶活力仅为3.7%;同时,贮藏期间的AV、POV、MDA指标明显优于对照样,因此大大延长了麦胚的贮藏期.     

热处理对大豆蛋白质品质的影响

对中国和阿根廷大豆在实验室的蒸汽炒锅内于100℃、118℃和136℃下蒸汽处理不同时间,测定未处理和经处理的大豆样品中干物质（DM）、粗蛋白质（CP）、胰朊酶抑制因素活性活性（TIA）、蛋白质分散指数（PDI）和活性赖氨酸含量。实验结果表明,不同产地的大豆需不同的热处理条件以改善其蛋白质品质。