Thermal Degradation of Paralytic Shellfish Poison

Components of paralytic shellfish poison (PSP) were heated under various conditions, and examined for changes in toxicity and in HPLC and TLC behaviors. The thermal degradation of PSP components progressed as a first order reaction, at different rates depending upon component and temperature. A mixture of gonyautoxin 2 and gonyautoxin 3 when dissolved in water and heated at 100°, 110°, and 120°C (180 min) retained 39, 17, and less than 3%, respectively, of initial toxicity. A mixture of gonyautoxin 1 and gonyautoxin 4 was more therrnolabile; i.e. it retained little toxicity when heated at 120°C for 60 min. HPLC and TLC analyses demonstrated that heating under those conditions converted PSP components into other substances.     

The production of ochratoxin A and citrinin in barley

The production of ochratoxin A by Aspergillus ochraceus and of ochratoxin A and citrinin by Penicillium viridicatum growing on previously sterilised barley for 200 days at 5, 10 and 20°C and a water activity of 0.85 is reported. A. ochraceus did not grow at 5°C, multiplied slowly at 10°C but did not produce toxin. At 20°C the organism multiplied more quickly and produced ochratoxin after 19 days, which slowly disappeared over the next 150 days. P. viridicatum grew slowly at 5°C but did not produce any toxin. It multiplied at 10°C and produced ochratoxin A which was only detectable during the period from 100 to 150 days. At 20°C both ochratoxin A and citrinin were produced. Ochratoxin A was detected after 10 days and was still present after 240 days, whereas citrinin was produced in large quantities between 118 and 129 days and then rapidly disappeared.     

Heat treatment of coconut meats and coconut meal

In attempts to determine the heat tolerance of coconut meats and coconut meal, samples were subjected to several temperatures far varying lengths of time. Properties evaluated were browning (by visual observation), odour, lysine destruction, protein solubility at pH 2, 8 and 10·5, and nitrogen solubility index. Solubility studies suggest that fresh coconut meats can tolerate up to 100°c air temperature (coconut layer temperature, 78–83°c) without significant loss of protein solubility. At 110°c air temperature, there is loss of solubility at pH 2 and 8, and at 120°c protein solubility significantly decreases under all the pH conditions examined. Data indicate a marked loss of lysine availability upon heating coconut meats with hot air at 120°c. Coconut meal can tolerate 105°c air for at least 60 min without significant loss of protein solubility. At higher temperatures (120°c for 15 min or longer), protein solubility decreased. Unavailable lysine data indicate that heating at 120°c for 60 min markedly decreases lysine availability.     

Ohmic Heating Behaviour of Cabbage and Daikon Radish

Shredded cabbage (50 % v/v) and Daikon radish cubes (57 % v/v) with different salt concentrations (0.15, 0.5, 1, 1.5, and 1.85 %) were heated from 30 to 70 °C in a static ohmic heating cell at different voltages (65, 80, 100, 120, and 135 V) and frequencies (60, 2070, 5030, 7990, and 10,000 Hz) to evaluate their ohmic heating behaviour. Radish heated under 1.5 % salt, 120 V and 7990 Hz or 1 % salt, 135 V and 5030 Hz conditions gave the shortest heating time of 6 min from 30 to 70 °C, and cabbage gave the longest time of 128 min at 0.15 % salt, 100 V, and 5030 Hz. Regression models of heating rate as a quadratic function of the sample temperature gave R² >0.98. The general trend observed was that the magnitude of the heating rate increased with frequency at high voltage but decreased at low voltage for cabbage, while the opposite trend was observed for radish. Heating was more efficient at higher salt concentration and applied voltage. Radish heated more rapidly than cabbage. A slight slope change was observed in all cases between 50 and 60 °C. The response surface models revealed linear, cross products and quadratic effects to be significant with R ² over 0.98.     

Thermal Aggregation and Dynamic Rheological Properties of Pacific Whiting and Cod Myosins as Affected by Heating Rate

Thermal aggregation of cod myosin and Pacific whiting myosin were compared at different heating rates. Turbidity of Pacific whiting started to increase at 30°C and decreased at >50°C, and fluorescence intensity of ANS-myosin of both species was greater at slower heating rates at 20–80°C. Storage modulus (G′) of cod myosin gradually increased as temperature increased resulting in more elastic gel at slower heating rates. G′ of whiting myosin rapidly increased at 30°C, maximized at 45–48°C and decreased afterward. The onset temperature of a decreased G′ shifted from 45°C to 49°C as heating rate increased from 0.5 to 2°C/min. Whiting myosin heated at 2°C/min retained more myosin heavy chain.     

Effect of Heat Treatment for Trypsin Inhibitor Inactivation on Physical and Functional Properties of Peanut Protein

Trypsin inhibitor (TI) inactivation in whole peanut kernels exposed to moist heat had a decimal reduction time (D) of 91 min at 100°C and 9.3 min at 120°C. When all processing times were converted to process time at 120°C using Z of 20°C, the composite D at 120°C was 10 min. Solubility decreased with heating to reach a minimum with 98% TI inactivation. Capacities to spontaneously absorb water and to gel were retained better on heating at 120°C than at 100°C for equal TI inactivation. The most functional protein was in kernels heated at 120°C for 10 min. When 20 or 30% meat protein in a meat loaf formulation was replaced with the latter peanut protein, the resulting loaf retained more fat and water and exhibited higher shearing strengths than all meat formulations.     

Influence of Preheating Skimmilk on Water-holding Capacity of Sodium Salts of Caseinates and Coprecipitates

The effect of different preheat treatments of milk on the water-holding capacity of the corresponding sodium caseinates made under laboratory conditions was investigated. Unheated skimmed milk, and milks heated under conditions ranging from 60°C to 120°C for 1 min, respectively, were used for the manufacture of the caseinates. Water-holding capacity was estimated using a method involving equilibration of the powder with excess water and measurement of the volume of released water. Water-holding progressively increased with heating, whereby with 120°C/1 min more than two-thirds of the dispersion volume tested was retained. The whey protein content of the caseinates also varied according to temperature and water-holding capacity.     

Heating and Storage Conditions Affect Survival and Recovery of Listeria monocytogenes in Ground Pork

The effect of heating rate, heating atmosphere, and meat age on survival of Listeria monocytogenes was examined in ground pork, as well as the ability of injured cells to recover during storage under air and vacuum packaging at 4 and 30°C. Significantly more survivors were observed when samples were heated at 1.3°C/min than at 8.0°C/ min. Cells inoculated into 3-month-old pork were more sensitive to heating than cells inoculated into fresh ground pork (D_62°C= 5.2 min and 7.7 min, respectively). More survivors were detected when the meat was heated aerobically than anaerobically. However, storage under vacuum at 4 or 30°C resulted in faster recovery compared with cells packaged in air. Thus, heating and packaging conditions affected ability of this pathogen to survive and recover after a heat process in pork.     

Thermal degradation of precursors and formation of flavour compounds during heating of cereal products. Part I. Changes of amino acids and sugars

Extracts from wheat, rye and barley malt have been used as a source for free amino acids and sugars in MAILLARD reaction studies. By means of special GLC techniques we have determined the content of 16 amino acids and 6 sugars during heating under controlled conditions; temperature, time and pH were used as variables. Large differences in the reactivity between the single amino acids were registered. Lysine as well as arginine, glutamic acid and proline decreased in high amounts within 15 min of heating at 120 °C. While glucose, maltose and maltotriose were reduced significantly during the thermic process with fructose an increase with time and temperature up to 120 °C was observed. Extreme pH values below 5 and above 7 caused high losses in amino acids. Increasing pH values supported the formation of fructose during heating.     

Rigidity and Viscosity Changes of Croaker Actomyosin During Thermal Gelation

Two types of thermal scanning rigidity monitors (TSRM) were developed which are nondestructive and capable of monitoring rigidity or viscosity changes during heating of proteins over a wide range of concentrations. Thermal transitions which occur during gelation of croaker actomyosin were studied by these TSRM devices and the Brookfield viscometer during constant rate heating (1°C/min). Gelation of actomyosin occurred only at protein concentrations above 5.5% under these conditions. In plots of rigidity versus temperature, three transitions were observed during gelation, occurring near 38°C 46°C and 60°C. At lower concentrations, only one peak was observed, occurring near 36°C. A relationship between the 36–38°C transition in rheological properties and the high temperature “setting” phenomenon of fish proteins is postulated.     

Pasteurization of intact shell eggs

The feasibility of pasteurization for destruction ofSalmonella enteritidisin artificially- inoculated intact shell eggs was investigated. Water-bath and hot air ovens were used for pasteurization of intact shell eggs under different conditions using these two heating methods, either individually or in combination. Eggs pasteurized in a 57°C circulating water-bath for 25 min gave reductions inS. enteritidisATCC 13076 of about 3 log cycles whereas heating at 55°C in a hot air oven for 180 min gave a 5 log reduction ofS. enteritidis. A combin?ation of the two methods (water-bath heating at 57°C for 25 min followed by hot-air heating at 55°C for 60 min) produced 7 log reductions inS. enteritidisATCC 13076 in shell eggs. Examination of lysozyme activity and other physical properties of egg white upon heating indicated that the overall functionality of pasteurized shell eggs are acceptable under the heating conditions defined in this study. This process may be used to produce safe, pasteurized shell eggs.sed     

Shear thinning and antithixotropic behavior of a heated cross‐linked waxy maize starch dispersion

Abstract

Cross‐linked waxy maize (CWM) starch dispersions (2.6%, w/w) were heated in the range 60°C to 80°C and in a retort at 120°C. All the heated dispersions exhibited shear‐thinning behavior except for that heated for 15 min at 60°C which showed slight shear‐thickening. The consistency index (K) increased with heating time and was exponentially correlated to the granule size and the notional volume fraction. CWM starch dispersions heated for 8, 15 and 30 min at 120°C exhibited counterclockwise (antithixotropic) shear rate‐shear stress hysteresis loops. Similar behavior was observed when dispersions were sheared in three continuous cycles and they became more viscous with each shear cycle. Clusters of granules were found in sheared retorted dispersions that may have been shear induced. Gelatinized granules viewed with SEM appeared to have folds and crevices which may have aided in cluster formation.     

Heat stability of endo-polygalacturonases of Mucoraceous spoilage fungi in relation to canned fruits

The heat resistance of endo-polygalacturonase (endo-PG) of the strawberry spoilage fungi, Rhizopus sexualis, R. stolonifer and Mucor piriformis, was compared to that of isolates of R. arrhizus, R. stolonifer and R. oryzae known to cause breakdown of canned apricots. All species produced endo-PGs in culture medium which showed marked heat tolerance and a bimodal heat stability. Heating for 10 min at temperatures between 30–120°C indicated that maximum inactivation occurred at 50–60°C. Stability increased from 70°C to 100°C and then declined, but in some cases activity remained even after heating at 120°C for 10 min. Similar trends in heat resistance were recorded for endo-PGs in infected tissue of apricot, peach, tomato and cherry fruits, whereas those in infected tissue of strawberry, raspberry and plum were rapidly inactivated at all temperatures above 40°C. The possible reasons for differences between fruits are discussed.     

Staphylococcus aureus Growth and Enterotoxin Production in Mushrooms

An enterotoxin A (SEA) producing strain of Staphylococcus aureus was inoculated onto mushrooms and incubated under simulated pre-and post-canning conditions. S. aureus grew and produced SEA in mushrooms incubated at 25°C in 10% to 20% NaCl. Growth and SEA production occurred when mushrooms were stored in plastic bags at 37°C, but not at 25°C. Mushrooms heat-processed at 121.1°C supported S. aureus growth and SEA production. No SEA was recovered from mushrooms inoculated with 1 or 10 ng SEA/g and heated at 121.1°C for 4.5 min. At higher inoculated SEA levels (100 and 1,000 ng/g), SEA was detectable after 10 min of heating. Staphylococcal enterotoxin could be present in canned mushrooms as a result of pre-, but more likely post-processing contamination.     

Effect of temperature–time pretreatments on the texture and microstructure of abalone (Haliotis discus hanai)

The effects of temperature/time pretreatments on the texture and microstructure of abalone (Haliotis discus hanai ) meat with the same myofibril extraction rate (60–66.7%) were investigated. The abalone samples were categorized into control and four treatment groups of different heating temperature/heating time combinations as 50°C/120 min, 60°C/10 min, 70°C/5 min, and 80°C/2 min, respectively. Compared to the control samples, the abalone samples heated at 60°C/10 min were the most tender (minimum shear force). It is clear that a sharp reduction in hardness was observed in heat treated abalone meat samples, compared to the raw samples. Nuclear magnetic resonance (NMR) showed that the water distribution pattern in abalone samples changed as they were experiencing different heat treatments. Particularly, the immobilized water components in samples heated at 60°C/10 min increased significantly. The textural properties of these samples evaluated after an 80 s‐reheating by microwave were of superior quality. It is concluded that the optimal condition for pretreatment abalone was 60°C/10 min, which could significantly improve the textural properties of preprocessed abalones.

Practical applications

Ready‐to‐eat foods can either be consumed directly, or further prepared according to consumers' preference. They are processed and packed following scientifically defined criteria to meet ready‐to‐eat requirements. For consumers, the quality of the food is one of the most important factors affecting purchasing decisions. Pretreatment through heating plays a key role in determining the eating quality of the product. Our study investigated the effects of pretreatment temperature and time on the food quality. These findings will establish optimal conditions for pretreating abalone to develop high‐quality ready‐to‐eat food products.

     

Formation of Amylose‐Lipid Complexes and Effects of Temperature Treatment. Part 1. Monoglycerides

The formation of amylose‐lipid complexes of form I (amorphous structure) and form II (crystalline structure) during heating was studied by differential scanning calorimetry (DSC) for a range of monoglycerides and for monoglyceride mixtures. The temperature treatment applied to amylose‐monoglyceride‐mixtures were either the first scan in DSC (10 °C/min, 15‐144 °C) or a prolonged heat treatment where the samples were kept at 100 °C for 24 h before being analysed in DSC. The temperature treatment influenced which type of complex was formed, and how much, whereas the thermal stability (as judged from the transition peak temperature) was only marginally influenced. It is shown in this study that all the investigated monoglycerides were able to give complex form I as well as complex form II, although the conditions for the formation differed between the monoglycerides. It was found that a simple DSC‐scan was enough for formation of complex form II for the shortest monoglycerides (glycerol monocaprin, glycerol monolaurin and glycerol monomyristin), whereas in case of the longer monoglycerides and monoglyceride mixtures the prolonged heat treatment was required for formation of complex form II. Moreover, the monoglyceride mixtures gave only form II at conditions where the individual components in the mixtures gave both form I and form II.     

Temperature influence on Penicillium citrinum Thom growth and citrinin accumulation kinetics

To study the temperature influence on both Penicillium citrinum growth and citrinin accumulation, a strain isolated from corn was cultured on Czapek agar with maize extract at 15, 20, 25 and 30 °C. Radial growth rate and lag phase were determined from the increase in colony diameter with time. The optimal temperature for P. citrinum growth was 30°C. Citrinin extracted from the agar medium was determined by thin layer chromatography. Citrinin accumulation kinetics were analyzed by fitting the data to curves generated by using a logistic function. The parameters obtained from this equation demonstrated, for all temperatures studied, that the maximum citrinin accumulation by P. citrinum on Czapek agar with maize extract was at about 30°C. At 37°C a rapid decrease in the citrinin concentration was observed after a maximal value was reached.     

Effect of Temperature Cycling on the Production of Patulin and Citrinin

Two strains of Peniciltium urticae (NRRL 2159A and 1952) and one strain of P. cltrinun (NRRL 5927) were used to investigate the effect of temperature Oycling on the production of patulin and citrinin. Temperature cycling (33–25°C, 33–15°C, and 25–15°C) delayed the rate of patulin biogenesis. As a general rule, cultures grown under cycling temmperature conditions produced less patulin than cultures grown a1 constant temperatures. The effect of temperature cycling (30–25°C, 30–15°C, and 25–15°C) on citrinin production was found to vary with the temperature combination.     

Changes in aromatic volatile composition of strawberry after high pressure treatment

The aromatic volatile compounds of high pressure treated strawberry coulis (Fragaria ananassa Gariguette) were analysed by capillary gas chromatography–mass spectrometry (GC–MS) and compared with aromatic volatile compounds of raw strawberry and heat-treated strawberry coulis. Characterisation of treated and untreated samples was achieved by applying principal component analysis to the chromatographic data. Aroma of strawberry was specifically identified by furaneol (2,5-dimethyl-4-hydroxy-furan-3-one) and nerolidol (3,7,11-trimethyl 1,6,10-dodecatrien-3-ol). No significant changes of all the aromatic volatile compounds were observed between untreated and high pressure-treated (200 and 500 MPa, 20°C, 20 min) strawberry coulis. On the other hand, changes appeared in the composition of aromatic compounds after an ultra high hydrostatic pressure treatment at 800 MPa (20 min, 20°C) and after a sterilisation (120°C, 20 min).     

Effect of thermal processing on available lysine,thiamine and riboflavin content in soymilk

Soymilk was heated over a range of temperatures (90–140°C) and times (0–6 h). The available lysine, thiamine and riboflavin content of the soymilk samples were determined. There was no significant change in available lysine during a 3 h heating period at 95°C. At elevated temperatures of 120 and 140°C, optimum heat processed soymilk gave higher measured values of available lysine than did soymilk processed at 95°C. Prolonged heating at 120 and 140°C caused a decline in available lysine. Kinetic data on the thermal degradation of thiamine and riboflavin in soymilk were fitted with first-order kinetics and the kinetic parameters were determined. © 1998 SCI.