Enhanced destruction of spoilage microorganisms in apple juice during continuous flow microwave heating

Destruction kinetics of two selected spoilage microorganisms, Saccharomyces cerevisiae and Lactobacillus plantarum in apple juice were evaluated under continuous flow microwave heating conditions and compared with conventional batch heating in a water bath. Inoculated apple juice was heated in a microwave oven (700 W, 2450 MHz) under continuous-flow conditions to selected exit temperatures (52.5–65°C). Aliquots of inoculated juice were also subjected to batch thermal treatments (50–80°C) in a well-stirred water bath. Time-temperature profiles obtained both during heating and cooling of test samples were used to correct both come-up and come-down times. The time-corrected D-values under microwave heating were 4.8, 2.1 and 1.1 s at 52.5, 55 and 57.5°C, respectively, for S. cerevisiae and 14, 3.8 and 0.79 s at 57.5, 60 and 62.5°C, respectively, for L. plantarum with corresponding z-values of 7 and 4.5°C. D-values under batch thermal heating were 58, 25, 10 and 1.9 s at 50, 55, 60 and 70°C, respectively, for S. cerevisiae and 52, 22, 8.4 and 1.2 s at 55, 60, 70 and 80°C, respectively, for L. plantarum with corresponding z-values of 13.4 and 15.9°C. Microbial destruction thus occurred much faster under microwave heating than under thermal heating suggesting some contributory enhanced effects to be associated with microwave heating.     

Continuous reactor for enzymic glycerolysis of butteroil in the absence of solvent

A continuous reactor was evaluated for lipase-mediated glycerolysis of butteroil in the absence of solvent. Lipase (from Pseudomonas cepacia) was immobilized by adsorption, followed by covalent coupling with glutaraldehyde, on a polypropylene sheet which was placed inside the reactor in a spiral wound configuration (axial-annular flow). Substrate feedstock was 2:1 (w/w) butteroil/glycerol and included 1% (w/w) lecithin to promote phase homogeneity. Reactor temperature was maintained at a minimum of 40 °C to prevent substrate/product solidification and attendant reactor fouling. Glycerolysis was found to be most efficacious at 45–55 °C, with 10.5% aqueous glycerol, and at reactor space times approaching 10 h. Under these conditions, >70% butteroil triacylglycerols were converted into a product mixture containing about 70% diacylglycerol and monoacylglycerol at a mass ratio of 2.1–2.2:1.     

Cooking rate, pH and final endpoint temperature effects on color and cook loss of a lean ground beef model system

To assess the effects of pH, heating rate and endpoint temperature on instrumental and visual color of ground beef, pH was adjusted to 5.2–6.4, samples were heated at 0.7°C or 3°C/min to 55, 60, 65, 70, 75 or 80°C in a water bath. Cooking rate had no effect on cook loss, instrumental or visual color. Regression equations for linear, quadratic and/or cubic effects of pH and/or endpoint temperature were significant for most color indices. Amount of variance explained by the model and R² was increased by adding the calculated percentages of metmyoglobin and/or deoxymyoglobin to the regression models. The predicted sensory brownness score (0=very pink, 7.5=intermediate pink/brown, 15=intense brown) for samples with pH 5.75 cooked to 70°C was 9.75. Samples with a pH of 5.5 achieved this brownness score at 67°C. Samples with a pH of 5.2 achieved this brownness at 58°C.     

The effect of temperature and humidity on the developmental period and mortality of Typhaea stercorea (L.) (Coleoptera: Mycetophagidae)

The development of Typhaea stercorea (L.) on kibbled wheat was investigated at temperatures from 15 to 30°C in combination with humidities from 70 to 90% r.h. Eggs hatched at 17.5–30°C but not at 15°C. Incubation periods ranged from 2.5 days at 30°C to 9.5 days at 17.5°C. Larval periods ranged from 9.7 days at 30°C, 90% r.h. to 83.6 days at 17.5°C, 80% r.h. and were more than doubled for each 10% decrease in humidity. At 70% r.h. all larvae died outside the temperature range 22.5–27.5°C. Mortality increased with decreasing humidity in the range tested. Pupal periods ranged from 2.9 days at 30°C, 80% r.h. to 13.8 days at 17.5°C, 90% r.h. At 70% r.h. the lowest temperature for pupal development was 25°C whereas at 90% r.h. it was 17.5°C. The results suggest that this species is essentially a mould feeder and confirm that it requires relatively high humidity to develop.     

Thermal inactivation of the frozen thawed traditional meat starter culture, Pediococcus pentosaceus, in a meat model system

The equation, y_(t) = y₍₀₎e^kt, was fitted (R = 0.9281, 0.9220 and 0.9117, respectively) to thermal inactivation data (55, 60 and 65 °C) of the traditional meat starter culture Pediococcus pentosaceus (10⁷ cfu/ml) in a meat model system. The population reduction constant (‘k’) increased (about 2.5- and 3-fold) with an increase in the treatment temperature (from 55 to 60 °C and from 60 to 65 °C, respectively). The Q₁₀ (55–65 °C) for ‘k’ was 7.63. Thermal treatments of 19.1, 9.0 and 3.1 min (55, 60 and 65 °C, respectively) reduced the population of P. pentosaceus by 2.0 logs. The value of ‘k’ and the duration of the thermal treatment played an important role in the extent of the inactivation of the culture. The “zero inactivation” temperature (T₀) for P. pentosaceus was 49.9 °C. About 5 logs of the culture would be destroyed at 63 and 68 °C within about 15.5 and 6.5 min, respectively.     

Effect of freezing and storage on quality factors in Hamburg and leafy parsley

Two types of parsley — the Hamburg cv Berli ska and leafy type cv Paramount — were frozen and stored at temperatures of −20 and −30 °C for 9 months. One half of the material was blanched before freezing and the other half was non-blanched. In 100 g fresh leaves of Hamburg parsley there were 20.0 g of dry matter, 310mg of vitamin C, 7.5mg of β-carotene, 203mg of chlorophyll, 30.8 mg N---NO₃ and 0.078 mg N---NO₂. For the leafy type the corresponding values were 17.3 g, 257 mg, 9.4mg, 68.5mg, and 0.077mg. The material blanched before freezing showed significant losses in the contents of vitamin C (47–51%), nitrates (22–33%), and nitrites (43–55%) and distinctly smaller ones but also significant in the case of dry matter. During freezing and storage of frozen products there were losses in vitamin C, β-carotene, and chlorophyll while the levels of nitrates and nitrites were variable. Particularly great losses of vitamin C and β-carotene were observed in the non-blanched frozen leaves stored at −20 °C. After 9 months' storage, frozen products preserved 10–44% of vitamin C, 37–91% of β-carotene, 78–95% of chlorophyll, and 78–153% of nitrates. Of the types of parsley analyzed the Hamburg type was a better raw material for freezing because of a significantly higher content of vitamin C and chlorophyll and significantly less nitrates in frozen products. When the storage temperature was −30 °C, the blanching of leaves was not necessary, although it helped their pressing into cubes.     

Survival of enterohaemorrhagic Escherichia coli O157:H7 strain in Turkish soudjouck during fermentation, drying and storage periods

Soudjouck (a kind of Turkish sausage) batter was inoculated with Escherichia coli O157:H7 at a level of 10⁵ colony-forming unit (CFUg) and kept overnight at 4°C. After stuffing the soudjouck batter into natural casing, fermentation was carried out at 24±2°C and 90–95% relative humidity (RH) for 3 days with subsequent drying at 22±2°C and 80–85% RH for 5 days. Then, half of soudjouck samples were vacuum-packed in polyethylene bags and the rest were kept open. All samples were stored at 4°C (55% RH) for 3 months. E. coli O157:H7 and lactic acid bacteria counts, moisture contents and pH values of the samples were determined during fermentation, drying and storage periods. Results showed that count of E. coli O157:H7 decreased by 3 log unit during fermentation and drying periods. It was observed that this pathogen survived longer in vacuum-packaged samples (more than 2 months) than non-vacuum samples (more than 1 month).     

Life history studies of internally feeding pests of stored sorghum: Sitotroga cerealella (Ol.) and Sitophilus oryzae (L.)

A laboratory study of the ecology of single species populations of Sitotroga cerealella (Olivier) and Sitophilus oryzae (L.) was made at 3 temperatures (25, 30 and 35°C) and 3 relative humidities (60, 70 and 80% r.h.). The effects of 2 lower humidities (40 and 50% r.h.) on both species were also studied at 30°C. The optimum conditions for multiplication of S. cerealella were found to be 25–30°C and 60–80% r.h. while for S. oryzae the optimum was more clearly defined (30°C and 80% r.h.). However S. cerealella could tolerate a higher temperature (35°C) and lower humidities (40 and 50% r.h. at 30°C) than S. oryzae. The results are compared with those of other workers on sorghum and other cereals, and discussed in relation to the distribution of the two species in Sudan.     

Sorption isotherms of salted minced pork and of lean surface of dry-cured hams at the end of the resting period using KCl as substitute for NaCl

The effect of KCl on sorption isotherms was determined on salted minced meat (with 0%, 30% and 100% molar substitution of NaCl by KCl) at 5 °C and 25 °C and meat from a 3 mm thick slice from the surface of dry-cured hams (with 0% and 35% molar substitution of NaCl by KCl) held at 70–75%, 75–80% and 80–85% air relative humidity during the resting period.

The sorption isotherms were determined gravimetrically by exposing the meat samples to several atmospheres of known relative humidity controlled by different saturated salts according to the COST90 method. The sorption equipment consisted of a chamber containing 11 containers, covering the water activity (a_w) range from 0.112 to 0.946 at 25 °C. The hermetically closed sorption containers filled with KCl and minced meat samples were irradiated at 3 kGrey (gamma irradiation ⁶⁰Co). The water content at equilibrium was higher in minced meat with NaCl than in minced meat with KCl (100% molar substitution of NaCl by KCl) at 5 °C within the range of 0.4313 and 0.7565 a_w. However, when substitution was 30% in minced meat and 35% in hams the isotherms were similar to isotherm without substitution.     

Exposure of Ephestia cautella (Wlk.) pupae to carbon dioxide concentrations at different relative humidities: The effect on adult emergence and loss in weight

The effects on mortality and loss in weight caused by 21, 51 and 88% carbon dioxide in combination with relative humidities of 20–22, 54–55, and 95–96% were tested on 0–24 hr old Ephestia cautella pupae, at 26°C. Exposure times ranged from 1 to 6 days. At 54–55%, and 20–22% r.h. pupal mortality was high for all carbon dioxide concentrations used, while at 95% r.h. total mortality was obtained only at the highest carbon dioxide concentration tested. At carbon dioxide concentrations of 51 and 88% a 9–11% concentration of oxygen was present. At 20–22% and 54–55% r.h. loss in weight of pupae exposed to carbon dioxide concentrations of 21% and higher was very pronounced. At 95–96% r.h., none of the treatments resulted in loss in weight exceeding 16% after six days of exposure. A 95% mortality curve represents the interrelated effect of carbon dioxide and relative humidity on the moth pupae. The fumigant effect of carbon dioxide is discussed.     

The influence of relative humidity and thermal acclimation on the survival of adult grain beetles in cooled grain

The influence of humidity and thermal acclimation on the survival of Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus granarius, S. oryzae and Tribolium castaneum in cooled wheat or flour at 45 and 70% relative humidity was studied in the laboratory. Young adults were held continuously at 30 or 32°C; cooled gradually to 13.5°C and held at that temperature; cooled gradually to 9°C and held at that temperature; or transferred directly to 9°C.

Survival at low temperatures differed, often considerably, between species, being generally shortest in T. castaneum (0.7–16 weeks) and longest in S. granarius (5–40 weeks). There was considerable interaction between the effects of temperature and humidity, with survival being, to varying degrees, shorter in 45% r.h. than in 70% r.h. At 45% r.h., an equilibrium relative humidity common in Australian storages, all species survived when the grain was cooled to 13.5°C but only S. granarius survived 26 weeks in grain cooled to 9°C.

Chill-coma temperature and acclimation temperature were linearly related in all species at each humidity. Neither the slopes nor intercepts of the relationships were influenced by humidity. There was generally an inverse relationship between survival and chill-coma temperature.

At 45% r.h., the increase in survival at 9°C attributable to acclimation ranged from 2-fold in S. oryzae (0.9 weeks) to 3.5-fold in C. ferrugineus (3.8 weeks). Corresponding values for beetles at 70% r.h. ranged from 2.3-fold in R. dominica (2.4 weeks) to 7.9-fold in C. ferrugineus (6.9 weeks).     

Pressure-induced thermotolerance of Lactobacillus rhamnosus GG

Non-lethal high pressure treatment was evaluated regarding its potential of inducing heat resistance in Lactobacillus rhamnosus GG. Pressure pre-treated cells (at 100 MPa and 37 °C for 10 min) showed higher survivability than untreated ones when both were heat treated at 60 °C. Upon exposure to this lethal temperature for 5 min, cells survived better by 1.5 log-cycles in comparison to control group, when they were previously pressure treated at 100 MPa and 37 °C for 10 min. Apparently, only short-time heat resistance was positively affected by such pressure pre-conditioning step since at prolonged holding time at 60 °C (more than 7 min), no significant differences regarding the inactivation rate was observed. Various pressures (100–200 MPa), temperatures (37–50 °C), and holding times (5–10 min) were systematically investigated. The findings can serve as indications towards optimizing production of probiotic starter cultures using spray-drying.     

Temperature shows greater impact on bovine Longissimus dorsi muscle glycogen debranching enzyme activity than does salt concentration

The degradation of glycogen progresses by the co-operation of two enzymes: glycogen phosphorylase (phosphorylase) and glycogen debranching enzyme (GDE). We studied the effect of temperature (4–42 °C) and salt concentration (0–3% NaCl) on bovine M. longissimus dorsi GDE activity. GDE activity (n = 4) decreased significantly with decreasing temperature from about 40–4 °C. GDE exhibited 52% activity at 25 °C and 11% at 4 °C compared to its optimum activity measured at 39 °C. In rapidly chilled meat, the reduction in GDE activity may substantially delay the rate of glycolysis. However, residual GDE activity at 4 °C seems sufficient to enable the attainment of normal ultimate pH if the available time is long enough. An increase in salt concentration from 0% to 2% and to 3% induced a significant (P < 0.001) increase in the ultimate pH of ground bovine meat (n = 6), but showed no effect on GDE activity.     

Effects of temperature and humidity on development of four pyralid moth pests of stored products

The development of Plodia interpunctella, Ephestia cautella, E. kuehniella and E. elutella was followed carefully at selected temperatures. Infertility prevented successful breeding of the latter two species at 30°C. The first two species bred successfully at 30°C, failed to complete development at 15°C, and, at 20–30°C, completed development more quickly than the other two. All species took longer to develop and survived less well at 25% r.h. than at 70% r.h., and their pupal stages lasted about twice as long as the egg stages at temperatures allowing development of both. At 25°C, the pupal stage lasted about 9 days in P. interpunctella and E. cautella, 11–12 days in E. kuehniella and about 13 days in E. elutella.

In all species other than E. elutella, eggs held at 25°C became more tolerant of cold when aged over 1 day. Younger eggs of P. interpunctella were less tolerant of cold than any eggs of the other species, and were killed outright by holding for 19 days at 15°C.

Stocks of all four species recently collected from the field generally tolerated low r.h. and low temperature a little better than laboratory stocks, but at higher temperatures developed from egg to adult a little more slowly.     

Physico-chemical and organoleptic properties of patties from hot, chilled and frozen goat meat

The effects of processing hot versus chilled goat meat, as such and after freezing in chunk or mince forms, were studied in relation to physico-chemical and organoleptic properties of patties. The differences in the pH of the meat samples were non-significant (P < 0·05) at 3–4 h post mortem (PM) at room temperature (30°C) and after 24 h at 4°C. The yield of the broiled patties, prepared from hot meat at 3–4 h PM, was significantly lower (P<0·05) as compared to those from chilled meat. However, this trend was reversed, if processing of hot meat into patties was done within 1–2 h PM. Freezing of chilled meat in chunk or mince forms gave significantly higher (P < 0·05) cooking yields than freezing of hot meat in similar forms.

The organoleptic scores of the raw-cooked patties were similar for all treatments. Freezing of precooked patties at −10°C for 10 days, thawing and reheating did not reduce most of the sensory scores significantly (P<0·05). Moisture, protein and fat contents of the broiled patties were not significantly (P<0·05) affected by the treatments. Standard plate count of hot versus chilled meat, for all levels of processing and storage, were within acceptable limits.     

Calpains from thaw rigor muscle

Pre-rigor beef M. Longissimus lumborum and diaphragma were frozen at −70 °C and thawed at different temperatures and the activities of extracted calpains and the toughness of heated meat compared with those in chilled muscle.

Fresh muscle contained about 14 μg of μ-calpain/g and was unaffected by freezing, but was reduced after thawing. Rapid thawing at 30 °C for 20 min reduced the μ-calpain to 14%. When cooked from the frozen state, extensive shortening occurred and tender meat was obtained.

By storing at −3 °C for 1 day, thaw-shortening was prevented, but tougher meat obtained. The μ-calpain decreased to 70% whilst the m-calpain was unaffected. Toughness decreased after further storage at −3 °C, as did the μ-calpain. The latter changes were similar to those during development of rigor mortis and ageing of non-shortened meat stored at 4 °C. Variation in calpain activity, rather than in sarcomere length, are likely to be the cause of toughness variation in thaw rigor muscle.     

Enthalpy-Entropy compensation in food vapor adsorption

Enthalpy-entropy compensation was analysed for sorption isotherms of potatoes, macadamia nuts, apricots, figs, currants, prunes and raisins. Plots of (ΔH_dif)_T vs (ΔS_dif)_T for potatoes and macadamia nuts presented two isokinetic temperatures: T_B1 = 272.0 ± 57.7 K (− 1 °C) for potatoes, T_B1 = 265.0 ± 18.8 K (− 8 °C) for macadamia nuts and T_B2 = 382.5 ± 7.3 K (109.5 °C) for both products. The first isokinetic temperature (T_B1) appeared only at the upper portion of the temperature range tested (50, 60 and 70 °C for potatoes and 50 and 60 °C for macadamia nuts). The two isokinetic temperatures observed for potatoes and macadamia nuts suggested that during the initial stages at low a_w T_B1 is controlled by changes in the entropy of water, whereas the second isokinetic temperature (T_B2) is considered to be enthalpy-controlled. Dried fruits presented only one isokinetic curve T_B = 315.7 ± 3.5 K (42.7 °C), for raisins, currants and figs (75.2–82.3% d.b. sugars) and T_B = 317.7 ± 4.6 K (44.7 °C) for prunes and apricots (51.5–54.5% d.b. sugars), indicating an enthalpy-controlled adsorption process for the whole range of moisture contents covered.     

Some influences of storage fungi, temperatures and relative humidity on the germinability of grass seeds

Seeds of Poa pratensis, Festuca rubra, F. arundinacea, and Lolium multiflorum were stored at 10, 20, 30, or 35°C, and at 35, 55, 75, or 95 per cent r.h. for up to 12 months. Samples stored at 30°C and 95 per cent r.h. and 35°C and 75 or 95 per cent r.h. decreased in germinability after 2 months of storage. At 20°C and either 75 or 95 per cent r.h., seeds decreased more slowly in germinative ability than at the higher temperatures but this decrease was appreciable. Seeds stored at 10°C and at 35, 55, 75, or 95 per cent r.h. germinated well after 12 months.

Equilibrium moisture content of the seeds after storage at 35 to 75 per cent r.h. for 2, 4, and 8 months varied little among the four species at each relative humidity level and was not affected by temperature in the range of 10–35°C.

Fungi of the Aspergillus glaucus group could not always be isolated from large numbers of seeds in lots that had declined in germinability. Seeds of all four grasses apparently carried superficially-borne species of the A. glaucus group (primarily A. amstelodami) in a ‘dormant’ state at harvest. Members of this group were isolated from substantial numbers of seeds that had been stored for 3 months at 30°C and 75 per cent r.h. These fungi were not isolated from seeds stored for the same length of time at 30°C and 35 per cent r.h.; however, field fungi grew from many of these seeds.     

The strength and stiffness of perimysial connective tissue isolated from cooked beef muscle

Thick transverse slices of bovine M. semitendinosus were cooked for 1 h at 50°–90° and then cooled. Perimysial connective tissue was dissected from the cooked meat and subjected to mechanical testing in a small-scale device. The initial ‘toe’ region of the J-shaped load-extension curve was progressively lost with increasing temperature, the curve becoming more nearly linear after cooking at 90°C. These effects are explained on the basis of the progressive straightening out of the crimps from the collagen fibres, the crimps becoming finally lost at approximately 70°C. The final stiffness of the perimysium at greater extensions was unchanged at higher temperatures. Breaking strength increased from raw to cooked at 50°C, thereafter decreasing at cooking temperatures up to 90°C. it is proposed that this technique of testing isolated perimysium gives a valuable means of directly measuring the effects of cooking, or other treatments, on the intrinsic properties of perimysial collagenous material. Quantitative knowledge of these will help to determine its contribution to the overall mechanical properties, and hence eating quality, of cooked meat.     

Low temperature storage of the predatory mite Cheyletus eruditus (Schrank) for future use in biological control

Populations of the predatory mite Cheyletus eruditus (Schrank) survive at temperatures ranging from −1·7 to +2·0°C and relative humidities of 80–90% for 5–6·5 months and retain their ability to reproduce upon transfer to favourable conditions. Populations obtained from natural aggregations and preserved under low temperatures could be used for the biological control of stored product mites.