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.     

SUPERCRITICAL CARBON DIOXIDE TREATMENT TO INACTIVATE AEROBIC MICROORGANISMS ON ALFALFA SEEDS

The supercritical carbon dioxide (SC-CO₂) process involves pressurizing CO₂ in a chamber which generates liquid phase of carbon dioxide. Pressurized liquid CO₂ has a strong extraction capability of organic and inorganic compounds. The recent studies have also demonstrated that antimicrobial effect of SC-CO₂ due extraction some cellular components of microorganisms. The efficacy of a supercritical carbon dioxide treatment on alfalfa seeds contaminated with Escherichia coli K12 was tested at 2000, 3000, and 4000 psi at 50C. Samples were treated for 15, 30, and 60 min at each pressure. After pummeling the seed samples in 0.1% peptone water, the initial and final Escherichia coli and total aerobic bacteria on the seeds were determined by plating on 3M Petri Films. After 48 h of incubation at 37 C, the colonies were enumerated. Treated seeds were evaluated in terms of germination characteristics. For aerobic plate count, the effect of pressure in the range of 2000–4000 psi was not statistically significant (p > 0.05) even though 85.6% inactivation was achieved at 4000 psi for 60 min. For E. coli, the reductions for 2000, 3000, and 4000 psi treatments for 15 min were 26.6, 68.1, and 81.3%, respectively. As the time was increased from 15 to 60 min at 4000 psi, the percent E. coli reduction increased from 81.3% to 92.8%. The percent germination for all treatments was over 90%. There was no significant difference (p > 0.05) in the germination rate of treated and untreated seeds. Supercritical carbon dioxide treatments demonstrated a reduction of E. coli K12 and total aerobic counts without affecting the germination characteristics of alfalfa seeds (p < 0.05). This study was a step in the direction of improving safety of alfalfa seeds used to produce fresh sprouts, which have been the cause of several outbreaks.     

EFFECT OF HEAT TREATMENT ON VISCOSITY OF YOLK

SUMMARY– Apparent viscosity readings at different shear rates for yolk or albumen-containing yolk in the native or heated conditions were obtained by a Wells-Brookfield microviscometer. The viscosity-shear rate curves for these yolk samples are typical for a pseudoplastic, non-Newtonian fluid. The apparent viscosity of native yolk with a solids content of 52.5% dropped gradually from 23 to 18 poises with an increase in shear rate from 1.9 to 76.8 sec^-1. The apparent viscosity of pasteurized yolk (65.6°C for 3 min) dropped drastically from 200 to 100 poises with an increase in shear rate from 1.9 to 19.2 sec^-1. Addition of thin albumen at levels of 5, 10 and 20% to native yolk brought about a considerable decline in the viscosity. The heat damage to the albumen-containing yolk as reflected by viscosity increase was reduced as the content of thin albumen increased. The viscosity increase of urea-treated yolk and yolk with 5 and 10% thin albumen was related to the temperature of heat treatment prior to urea addition.     

EFFECT of pH and ENZYMATIC TREATMENT ON MICROFILTRATION and ULTRAFILTRATION of TANGERINE JUICE

Tangerine (Citrus reticulata blanco) juice clarification by crossflow microfiltration and ultrafiltration using polysulphone flat sheet membranes with nominal molecular weight cut off of 25,000, 50,000, 100,000 and 0.1 μm, 0.2 μm pore sizes was studied. the juice was pretreated by polygalacturonase and pH adjustment. the treated juice was clarified with a laboratory scale filtration unit with effective filtration area of 14 cm². Filtration conditions were transmembrane pressure of 93 to 194 kPa, crossflow velocity of 0.96 to 3.5 m/s and 25°C. Membrane performance was evaluated in terms of volume flux and clarity (% transmittance) of the permeate. Pretreatment of the juice by polygalacturonase and adjustment to pH 2 with HCl resulted in a clearer supernatant than enzyme treatment alone. Maximum flux was obtained with the 0.1 μm microfiltration membrane. Flux increased with transmembrane pressure and crossflow velocity. Flux at 194 kPa and 3.5 m/s was 69 L per square meter per hour. Permeate clarity was better at higher transmembrane pressure and lower velocity, due to the effect of the polarized/fouling layer of solute on the membrane surface, which acted as a secondary “dynamic” filter.     

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.