High‐pressure processing‐induced conformational changes during heating affect water holding capacity of myosin gel

This study aimed to investigate the effects of high‐pressure processing (HPP) (0.1‐400 MPa for 9 min) on the water holding capacity (WHC) of heat‐induced rabbit myosin gel and structural changes during thermal treatment (25–75 °C). HPP at 100 MPa significantly increased the WHC (P < 0.05) and formed more regular and homogeneous three‐dimensional network. Myosin tails at 100 MPa unfolded completely during the thermal treatment, which was beneficial to form a high WHC gel network. However, myosin pressurised at 200 MPa and above formed a weak gel. Their heads were already aggregated before heating, preventing from subsequent thermal denaturation and aggregation. With the temperature increasing, unfolding of myosin tails was not sufficient for a filamentous network formation. These results suggested that HPP could modify the myosin structure and affect the gel formation during heating. The 100 MPa was the optimum pressure level for the WHC of rabbit myosin gel.     

Microwave Processing: Current Background and Effects on the Physicochemical and Microbiological Aspects of Dairy Products

Overheating is still a major problem in the use of conventional heating for milk and various dairy products, because it leads to the lowering of quality and sensory and nutritional values. Microwave (MW) heating has been credited with providing superior‐quality dairy‐based products with extended shelf‐life, representing a good alternative to conventional heat treatment. The main drawback of MW heating refers to nonuniform temperature distribution, resulting in hot and cold spots mainly in solid and semisolid products; however, MW heating has been shown to be suitable for liquid foods, especially in a continuous fluid system. This review aims to describe the main factors and parameters necessary for the application of MW heating technology for dairy processing, considering the theoretical fundamentals and its effects on quality and safety aspects of milk and dairy products. MW heating has demonstrated great ability for the destruction of pathogenic/spoilage microorganisms and their spores, and also inactivation of enzymes, thereby preserving fresh characteristics of dairy products.     

Physico‐chemical and functional properties of proteins from green mussel (Perna viridis) during ice storage

The effect of ice storage on the properties of proteins from green mussel (Perna viridis) has been investigated. Ice storage of green mussel for a period of 19 days revealed a marginal increase in moisture and decrease in total nitrogen content. There was significant reduction (P < 0.05) in non‐protein nitrogen content and calcium activated adenosine triphosphatase enzyme activity. The solubility of the total proteins in high ionic strength buffer decreased marginally. The ice storage of green mussel had a significant effect on association‐dissociation/denaturation phenomenon of proteins as revealed by gel filtration profile, reduced viscosity values and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) pattern. The dynamic viscoelastic behaviour of green mussel meat in the temperature range of 30–90 °C revealed higher storage modulus (G′) values at a later part of ice storage. The emulsion capacity of green mussel did not show significant variation (P < 0.05) during ice storage. Copyright © 2006 Society of Chemical Industry     

Kinetics of sensory quality changes in soymilk during thermal processing,by parametric and non‐parametric data analyses

Soymilk was subjected to various heat treatments at 90, 120 and 140 °C for various lengths of time. The colour and flavour of the soymilk samples were evaluated by a sensory panel consisting of eight semi‐trained assessors on (1) a 9‐unit hedonic scale, with analysis based on the assumption that the units are equidistant, and (2) a 15‐point hedonic ‘Smiley’ pictorial scale, the results being analysed non‐parametrically. The proportion (%) of ratings higher than or equal to/higher than the overall median of the samples was used as a rigorous estimate of product quality. These values were used to determine the colour and flavour changes in heated soymilk and their temperature dependence. The Z‐values derived from the parametric and non‐parametric analyses were in close agreement, ranging from 31 to 33 °C and from 30 to 32 °C for colour and flavour respectively. © 2000 Society of Chemical Industry     

Mitochondrial DNA Fragmentation as a Molecular Tool to Monitor Thermal Processing of Plant‐Derived,Low‐Acid Foods,and Biomaterials

Cycle threshold (Ct) increase, quantifying plant‐derived DNA fragmentation, was evaluated for its utility as a time‐temperature integrator. This novel approach to monitoring thermal processing of fresh, plant‐based foods represents a paradigm shift. Instead of using quantitative polymerase chain reaction (qPCR) to detect pathogens, identify adulterants, or authenticate ingredients, this rapid technique was used to quantify the fragmentation of an intrinsic plant mitochondrial DNA (mtDNA) gene over time‐temperature treatments. Universal primers were developed which amplified a mitochondrial gene common to plants (atp1). These consensus primers produced a robust qPCR signal in 10 vegetables, 6 fruits, 3 types of nuts, and a biofuel precursor. Using sweet potato (Ipomoea batatas) puree as a model low‐acid product and simple linear regression, Ct value was highly correlated to time‐temperature treatment (R² = 0.87); the logarithmic reduction (log CFU/mL) of the spore‐forming Clostridium botulinum surrogate, Geobacillus stearothermophilus (R² = 0.87); and cumulative F‐value (min) in a canned retort process (R² = 0.88), all comparisons conducted at 121 °C. D₁₂₁ and z‐values were determined for G. stearothermophilus ATCC 7953 and were 2.71 min and 11.0 °C, respectively. D₁₂₁ and z‐values for a 174‐bp universal plant amplicon were 11.3 min and 9.17 °C, respectively, for mtDNA from sweet potato puree. We present these data as proof‐of‐concept for a molecular tool that can be used as a rapid, presumptive method for monitoring thermal processing in low‐acid plant products.     

Recent developments in applications of radio frequency heating for improving safety and quality of food grains and their products: A review

Abstract

Food grains constitute a vital part of the daily diet of the population worldwide, and are generally considered as safe products with high storage stability due to their low moisture contents. However, post-harvest losses (PHL) caused by insects, fungi, food-borne pathogens, and undesirable enzymes remain a major concern for the grain industry. Thermal treatments are commonly used to reduce the PHL of grains and their products without any chemical residues. Among which, radio frequency (RF) technology has been regarded as a promising alternative to traditional heating methods for improving safety and quality of food grains due to its fast, volumetric, and deep penetration heating characteristics. This review provided comprehensive information about principles of RF technology and its main applications including disinfestation, pasteurization, enzyme inactivation, drying, and roasting for processing food grains and their products. The methods to improve the RF heating uniformity and effects of RF heating on product quality were also reviewed. Finally, the current problems and recommendations for future work related to RF processing of grains and their products were discussed. This review would improve the understanding of RF heating for food grains and their products and promote the application of RF technology in the food grain industry.     

Plant‐based food and feed protein structure changes induced by gene‐transformation,heating and bio‐ethanol processing: A synchrotron‐based molecular structure and nutrition research program

Unlike traditional “wet” analytical methods which during processing for analysis often result in destruction or alteration of the intrinsic protein structures, advanced synchrotron radiation‐based Fourier transform infrared microspectroscopy has been developed as a rapid and nondestructive and bioanalytical technique. This cutting‐edge synchrotron‐based bioanalytical technology, taking advantages of synchrotron light brightness (million times brighter than sun), is capable of exploring the molecular chemistry or structure of a biological tissue without destruction inherent structures at ultra‐spatial resolutions. In this article, a novel approach is introduced to show the potential of the advanced synchrotron‐based analytical technology, which can be used to study plant‐based food or feed protein molecular structure in relation to nutrient utilization and availability. Recent progress was reported on using synchrotron‐based bioanalytical technique synchrotron radiation‐based Fourier transform infrared microspectroscopy and diffused reflectance infrared Fourier transform spectroscopy to detect the effects of gene‐transformation (Application 1), autoclaving (Application 2), and bio‐ethanol processing (Application 3) on plant‐based food and feed protein structure changes on a molecular basis. The synchrotron‐based technology provides a new approach for plant‐based protein structure research at ultra‐spatial resolutions at cellular and molecular levels.     

Packaging under pressure: Effects of high pressure, high temperature processing on the barrier properties of commonly available packaging materials

High pressure thermal (HPT) processing has the potential to deliver quality benefits to a range of processed foods. By exploiting the rapid temperature increase/decrease that accompanies pressurization/depressurization, commercial sterilization of foods can potentially be achieved by HPT with an overall reduced thermal exposure compared with conventional thermal processing technologies. High pressure thermal sterilization (HPTS) of foods is yet to be commercialized, but during development of the technology some potential limitations have been raised about the suitability for HPTS of commercially available packaging materials developed for retort processing. Key requirements of packaging materials for thermally processed foods are the preservation of oxygen and water barriers during processing and for the duration of the shelf life of the food. We examined the barrier properties after HPT processing of eleven commercially available packaging materials developed for conventional thermal sterilization processes. We found that the barrier properties of vapor-deposited oxide and nylon containing films were compromised by the combination of high pressure (600 MPa) and high temperature ( 110 °C) which would be reasonably expected to be required to render food commercially sterile by HPT processing. However, the barrier properties of aluminium foil and PVDC–MA containing films were not significantly affected by HPT processing. All materials suffered cosmetic deformation of the outer surface to some degree and mechanisms for these changes are proposed.

Industrial relevance

Information on the barrier properties of flexible packaging suitable for foods sterilized by HPT processing has been scarcely reported. This study provides information on the barrier properties of commercially available, retortable films processed under high pressure/high temperature conditions and identifies candidate packaging based on barrier performance.     

Effects of homogenisation pressures on physicochemical changes in different layers of ultra‐high temperature whole milk during storage

The objective of this study was to investigate the effects of homogenisation pressures (10, 20, and 30 MPa) on the physicochemical changes in top, middle and bottom layers of ultra‐high temperature whole milk stored at 25 °C for 6 months. Fat separation, fat globule sizes, fat and protein contents, viscosity, free amino acids content and pH were analysed at an interval of 15 days. Results showed that higher homogenisation pressure retarded the differentiations of milk fat globule sizes, fat and protein contents and viscosity in different milk layers, but did not affect the final fat separation, proteolysis and pH.     

Chemical,antioxidant and sensory properties of tomato‐watermelon‐pineapple blends,and changes in their total antioxidant capacity during storage

A conductometric analysis of the effect of condensate of peroxides generated during lipid oxidation in an accelerated stability test was adapted to test the hypothesis that total antioxidant capacity of tomato products would sometimes increase during processing and in storage. Tomato pulp blends made from a mixture of tomato (Lycopersicon esculentum var Roma VF), watermelon (Citrullus vulgaris var Babylack) and pineapple (Ananas comosus var Smooth cayennes) were analysed for basic quality profiles of dry matter, Brix, titratable acidity (TTA) and pH, total reducing sugars, Component antioxidants phytochemicals and total antioxidant capacity. The lowest sensory score (overall impression) of 4.80 ± 2.59 was recorded for tomato juice while, blend TWP 111p had highest score of 6.20 ± 1.99. There was significant difference (P < 0.05) in the basic quality profile of the pulp blends except for TTA values (0.37 ± 0.02 to 0.45 ± 0.05) and 2‐Furfurals (2.47 ± 0.03 to 2.71 ± 0.01). The fresh blend of 50% tomato, 25% watermelon and 25% pineapple had the highest total antioxidant capacity of 3.69 ± 0.52 mg 100 mL^?1 catechin equivalent. The total antioxidant capacity of the stored pulp increased from 2.95 ± 0.13 to 6.22 ± 0.32 mg 100 mL^?1 catechin equivalent in pasteurised TWP 211p blend by 60 days when stored at 40 °C. Total antioxidant status of tomato‐based fruit mix increased during the first 80 days.     

Effects of storage conditions and acid solvent types on structural,mechanical and physical properties of kudzu starch (Pueraria lobata)‐chitosan composite films

Effects of acid solvents (acetic, lactic and malic acid) on properties of kudzu starch‐chitosan composite films were evaluated at −20 or 25°C during storage of 60 days. The yellowness of films enhanced, whereas water content and water vapour permeability of films declined with increasing storage time. Tensile strength of films choosing acetic and lactic acid as solvents, and solubility of all the films increased within 30 days thereafter decreased. Storage temperature had no impact on X‐ray diffraction, water content and solubility. Under the same storage conditions, the film using acetic acid as solvent presented the strongest mechanical property, the smallest solubility and the lightest colour. The film made from lactic acid solution was the most flexible and the yellowiest. The film with malic acid solvent showed the highest ordering degree, the lowest water content and the best water barrier property.     

Microwave Pasteurization of Cooked Pasta: Effect of Process Parameters on Texture and Quality for Heat‐and‐Eat and Ready‐to‐Eat Meals

Pasta presents a challenge to microwave processing due to its unique cooking requirements. The objective of this study was to determine the effects of microwave processing on pasta physicochemical and mechanical properties. Fettuccine pasta was parboiled for selected times, then pasteurized using a Microwave Assisted Pasteurization System and stored under refrigeration for 1 wk. Samples were analyzed using microscopy, mechanical testing, and chemical analyses after storage. While no significant differences were observed for free amylose among fresh samples, samples parboiled for ≤6 min had significantly higher free amylose, suggesting reduced starch retrogradation. Increased heat treatment increased degree of protein polymerization, observed in microstructures as increased gluten strand thickness and network density. Firmness and extensibility increased with increased parboil time; however, extension data indicated an overall weakening of microwave‐treated pasta regardless of total cooking time. Overall, microwave pasteurization was shown to be a viable cooking method for pasta.     

Effects of Ultra High Pressure,Pressing Time and HCl Concentration on Non‐thermal Starch Hydrolysis Using Ultra High Pressure

Effects of ultra high pressure (UHP), pressing time and HCl concentration on non‐thermal starch hydrolysis using ultra high pressure were investigated. As regards ultra high pressure, starch granules maintained their structure up to 450 MPa and were partially disintegrated at 600 MPa. Degree of hydrolysis did not change up to 450 MPa and dramatically increased at 600 MPa indicating that starch hydrolysis increased with increasing destruction of starch granules. Pressing time did not affect the degree of hydrolysis. However, degree of hydrolysis and destruction of starch granules increased with increasing HCl concentration up to 4 M. Gel permeation chromatography showed that the soluble fraction of starch formed by hydrolysis mainly consisted of maltooligomers and maltose. X‐ray diffraction pattern changed from A type to C type upon hydrolysis, otherwise it remained as A type. This work provides fundamental information of UHP processing for starch and shows a potential of non‐thermal UHP processing for a new starch hydrolysis method.     

Effects of UV‐C on antioxidant capacity,antioxidant enzyme activity and colour of fresh‐cut red cabbage during storage

Ultraviolet C (UV‐C) irradiation is a widely used nonthermal sterilisation method used to ensure the quality and safety of fresh and fresh‐cut produce. However, research focus of UV‐C has recently shifted from safety of sterilisation damage towards improvements in quality. Red cabbage (Brassica oleracea var. capitata f. rubra) is a widely consumed fresh‐cut vegetable. In this study, the effects of UV‐C irradiation on the antioxidant capacity, antioxidant enzyme activity and colour of fresh‐cut red cabbage were evaluated. The UV‐C decreased the L*, a* and b* values, and it turned the colour darker and increasingly blue. UV‐C increased the activity of four antioxidant enzymes and also stimulated the accumulation of flavonoids, glutathione and ascorbic acids. The antioxidant activity of UV‐C treatment was higher than in the control group. These results suggest that an appropriate dose of UV‐C may improve the antioxidant properties of fresh‐cut red cabbage.