Roopesh M. Syamaladevi

Effect of thermal treatments on phytochemicals in conventionally and organically grown berries

BACKGROUND Consumer demand for organic foods is increasing despite a lack of conclusive evidence of nutritional superiority of organically grown produce. The objective of this investigation was to evaluate the effects of thermal treatments on phytochemicals in conventionally and organically grown berries. Two cultivars of conventionally and organically grown red raspberries and blueberries were analysed for total anthocyanins, total and specific phenolic compounds and total antioxidant activity. Fresh berries were thermally processed into cans and juice/puree with and without blanching, and the changes in phytochemicals were monitored. RESULTS Total anthocyanin and phenolic contents of berries were not influenced by the agricultural production system. Total antioxidant activity of berries was also not influenced by the production system, but antioxidant activity varied significantly between cultivars. After canning, total anthocyanins decreased by up to 44%, while phenolic contents and antioxidant activity of both berries generally increased by up to 50 and 53% respectively. The level of changes in phytochemicals during berry puree/juice processing was influenced by blanching and type of berries. CONCLUSION Phenolic contents and antioxidant activities of berries increased while total anthocyanins decreased during canning. Blanching prior to puree/juice processing improved the retention of phytochemicals in blueberries.

Influence of Water Activity on Thermal Resistance of Microorganisms in Low‐Moisture Foods: A Review

A number of recent outbreaks related to pathogens in low-moisture foods have created urgency for studies to understand the possible causes and identify potential treatments to improve low-moisture food safety. Thermal processing holds the potential to eliminate pathogens such as Salmonella in low-moisture foods. Water activity (aw ) has been recognized as one of the primary factors influencing the thermal resistance of pathogens in low-moisture foods. But most of the reported studies relate thermal resistance of pathogens to aw of low-moisture foods at room temperature. Water activity is a thermodynamic property that varies significantly with temperature and the direction of variation is dependent on the product component. Accurate methods to determine aw at elevated temperatures are needed in related research activities and industrial operations. Adequate design of commercial thermal treatments to control target pathogens in low-moisture products requires knowledge on how aw values change in different foods at elevated temperatures. This paper presents an overview of the factors influencing the thermal resistance of pathogens in low-moisture foods. This review focuses on understanding the influence of water activity and its variation at thermal processing temperature on thermal resistance of pathogens in different low-moisture matrices. It also discusses the research needs to relate thermal resistance of foodborne pathogens to aw value in those foods at elevated temperatures.

Ultraviolet-C light inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on organic fruit surfaces

This study investigated UV-C light inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on the surface of organic apples, pears, strawberries, red raspberries and cantaloupes. Fruit surfaces spot inoculated with cocktail strains of E. coli O157:H7 and L. monocytogenes were exposed to UV-C doses up to 11.9 kJ/m(2) at 23 °C. Fruit surface roughness, contact angle, and surface energy were determined and correlated with UV-C inactivation kinetics. Results demonstrate that bacterial pathogens on fruit surfaces respond differently to UV-C light exposure. E. coli O157:H7 on apple and pear surfaces was reduced by 2.9 and 2.1 log CFU/g, respectively when treated with UV-C light at 0.92 kJ/m(2) (60s). For berries, the reduction of E. coli O157:H7 was lower with 2.0 (strawberry) and 1.1 log CFU/g (raspberry) achieved after UV-C treatment at 7.2 kJ/m(2) (8 min) and at 10.5 kJ/m(2) (12 min), respectively. Similarly, a higher reduction of L. monocytogenes was observed on apple (1.6 log CFU/g at 3.75 kJ/m(2)) and pear (1.7 log CFU/g at 11.9 kJ/m(2)) surfaces compared to cantaloupe and strawberry surfaces (both achieved 1.0 log CFU/g at 11.9 kJ/m(2)). L. monocytogenes shows more resistance than E. coli O157:H7. Inactivation rates were higher for less hydrophobic fruits with smoother surfaces (apples and pears) as compared to fruits with rougher surfaces (cantaloupe, strawberry and raspberry). Findings indicate that UV-C light can effectively reduce E. coli O157:H7 and L. monocytogenes populations on fruit and berry surfaces. However, surface characteristics influence the efficacy of UV-C light.

Water Sorption, Glass Transition, and Microstructures of Refractance Window– and Freeze-Dried Mango (Philippine “Carabao” Var.) Powder

Water sorption isotherms, glass transition, and microstructures of Refractance Window (RW)– and freeze-dried Philippine “Carabao” mango powders were investigated. Water sorption isotherms were developed by the isopiestic method, while thermal transition of the powders, at various water activities (a w = 0.11–0.86), was determined using differential scanning calorimetry (DSC). The sorption isotherms of RW- and freeze-dried (FD) mango powders exhibited a type III sigmoidal curve, showing higher and lower adsorption capacities above and below 0.5 a w , respectively. A significant difference (p < 0.05) in water content of RW- and freeze-dried mango powders for equivalent water activities was obtained above 0.5 a w . The onset glass transition temperature (T gi ) of RW- and freeze-dried mango powder solids decreased as the water content increased. There were no significant differences (p ≥ 0.05) in T gi of RW- and freeze-dried mango powder solids at constant water activities, except for a w = 0.86. Microscopic examination of mango powders indicated that freeze-dried mango powders exhibited greater surface area and porosity in comparison to RW-dried mango powders.

Physicochemical Properties of Encapsulated Red Raspberry (Rubus idaeus) Powder: Influence of High-Pressure Homogenization

Encapsulated red raspberry (Rubus idaeus) powders with gum arabic were produced using a spray-drying method. The raspberry puree samples were treated with and without high-pressure homogenizers prior to spray drying. The physicochemical properties of spray-dried raspberry powders were analyzed. The median particle size (X 50) of raspberry powder produced with high-pressure homogenized puree (14.6 µm) was smaller than raspberry powder produced without high-pressure homogenization applied to puree (18.3 µm). Glass transition temperatures and water contents of encapsulated raspberry powders were not significantly different (p > 0.05) at equivalent water activities. High-pressure homogenization of puree resulted in greater apparent density and porosity for encapsulated raspberry powder. Greater particle size resulted in higher hygroscopicity and water solubility index (WSI) for encapsulated raspberry powder produced without high-pressure homogenization of puree. Anthocyanins concentration was greater in raspberry powder pretreated with high-pressure homogenization although powder exhibited lower brightness, redness, and yellowness.

Storage effects on anthocyanins, phenolics and antioxidant activity of thermally processed conventional and organic blueberries

BACKGROUND Consumer demand for products rich in phytochemicals is increasing as a result of greater awareness of their potential health benefits. However, processed products are stored for long-term and the phytochemicals are susceptible to degradation during storage. The objective of this study was to assess the storage effects on phytochemicals in thermally processed blueberries. Thermally processed canned berries and juice/puree were analysed for phytochemicals during their long-term storage. RESULTS The phytochemical retention of thermally processed blueberries during storage was not influenced by production system (conventional versus organic). During 13 months of storage, total anthocyanins, total phenolics and total antioxidant activity in canned blueberry solids decreased by up to 86, 69 and 52% respectively. In canned blueberry syrup, total anthocyanins and total antioxidant activity decreased by up to 68 and 15% respectively, while total phenolic content increased by up to 117%. Similar trends in phytochemical content were observed in juice/puree stored for 4 months. The extent of changes in phytochemicals of thermally processed blueberries during storage was significantly influenced by blanching. CONCLUSION Long-term storage of thermally processed blueberries had varying degrees of influence on degradation of total anthocyanins, total phenolics and total antioxidant activity. Blanching before thermal processing helped to preserve the phytochemicals during storage of blueberries.

Water Diffusion from a Bacterial Cell in Low-Moisture Foods

We used a Ficks unsteady state diffusion equation to estimate the time required for a single spherical shaped bacterium (assuming Enterococcus faecium as the target microorganism) in low-moisture foods to equilibrate with the environment. We generated water sorption isotherms of freeze-dried E. faecium. The water activity of bacterial cells at given water content increased considerably as temperature increased from 20 to 80 °C, as observed in the sorption isotherms of bacterial cells. When the water vapor diffusion coefficient was assumed as between 10(-12) and 10(-10) m(2) /s for bacterial cells, the predicted equilibration times (teq ) ranged from 8.24×10(-4) to 8.24×10(-2) s. Considering a cell membrane barrier with a lower water diffusion coefficient (10(-15) m(2) /s) around the bacterial cell with a water diffusion coefficient of 10(-12) m(2) /s, the teq predicted using COMSOL Multiphysics program was 3.8×10(-1) s. This result suggests that a single bacterium equilibrates rapidly (within seconds) with change in environmental humidity and temperature.

Inactivation of Listeria monocytogenes on Frozen Red Raspberries by Using UV-C Light

In this study, the efficacy of UV-C treatment was determined on the reduction of foodborne pathogens on artificially contaminated frozen food surfaces. At first, the UV-C inactivation rates on 100 μl of the respective cocktails of Escherichia coli O157:H7, Salmonella , and Listeria monocytogenes covered underneath 0.5-cm-thick ice were examined. Simultaneously, the energy percentage of UV-C transmitted through the ice was determined. The experiments showed that more than 65% of the UV-C light energy passed through the ice and that UV-C susceptibility was in the descending order of E. coli O157:H7, Salmonella , and L. monocytogenes . L. monocytogenes , the most UV-C-resistant strain, was then selected to test on frozen raspberries. The UV-C inactivation kinetic data of L. monocytogenes were well described using the Weibull equation. During 720 s of UV-C exposure, with a total dose of 7.8 × 102 mJ/cm2, a 1.5-log CFU/g reduction of L. monocytogenes population on the surface of frozen red raspberries was noted. No significant differences in total anthocyanins, total phenolics, and total antioxidant activity were observed between UV-C-treated and untreated frozen berries immediately after treatment. At the end of 9 months of storage at -35°C, UV-C-treated berries had statistically lower total phenolics, higher total anthocyanins, and similar total antioxidant activity compared with untreated berries. This study shows that UV-C light can be used to reduce the L. monocytogenes population on frozen raspberries.

Molecular Weight Effects on Enthalpy Relaxation and Fragility of Amorphous Carbohydrates

Many food processing techniques such as dehydration, concentration, extrusion, and freezing produce amorphous foods that can be stored below their glass transition temperature (Wungtanagorn and Schmidt 2001). Below glass transition temperature (Tg), amorphous food constituents exist in a thermodynamically unstable nonequilibrium and disordered state. Isothermal storage/aging of glassy amorphous food components results in structural relaxations that achieve a more stable equilibrium state over extended time periods (Struik 1978). Since the equilibrium state is a low energy state, some of the energy is lost/relaxed in the nonequilibrium glassy amorphous state during isothermal storage of food components. This energy can be recovered in the form of enthalpy during the reheating of the glassy system by using a differential scanning calorimeter, since physical aging is a reversible process. The enthalpy recovered during reheating of the aged material system is a measure of the system’s molecular mobility at the selected aging temperature (Gupta et al. 2004). Structural relaxation in the glassy state of amorphous food components during isothermal storage/aging is also known as enthalpy relaxation/physical aging. Many macroscopic properties of glassy materials, such as volume, enthalpy, refractive index, electrical conductivity, and viscosity, change during physical aging (Struik 1978). The changes in macroscopic properties may adversely affect the physicochemical stability during the isothermal storage of low water amorphous foods and food constituents (Farahnaky et al. 2008).