Stability of vitamin C, color, and garlic aroma of garlic mashed potatoes in polymer packages processed with microwave-assisted thermal sterilization technology

The U.S. Army and NASA need ready-to-eat meals with extended shelf-life for military operations and future manned space missions. For traditional heat sterilization methods, aluminum foil laminated pouches are used to achieve a shelf-life of 3 to 5 years at room temperature. However, those packages are not suited for advanced thermal processing technologies based on microwave energy. This research investigated the effect of polymeric packaging materials on storage stability of garlic flavor, vitamin C, and color of garlic mashed potatoes processed with microwave-assisted thermal sterilization (MATS) technology. Three types of high-barrier metal oxide-coated polymer pouches were used for MATS process, designed to achieve lethality approximately F₀ = 6 min. Aluminum foil-based pouches were used for retort process as control. Results demonstrated that both oxygen and water vapor barrier properties (oxygen transmission rate [OTR] and water vapor transmission rate [WVTR]) of the polymer pouches were affected by MATS processing. OTR increased by three to nine times, while WVTR increased by 5 to 20 times after processing. The MATS process resulted in 13% to 16% vitamin C loss, while retort process resulted in 18% loss in garlic mashed potato. The kinetics of vitamin C indicated that metal oxide-coated high-barrier packages (after processing OTR <0.1 cc/m² .day; WVTR <1.0 g/m² .day) could replace aluminum foil-based pouches for MATS processed shelf-stable ready-to-eat garlic mashed potatoes. PRACTICAL APPLICATION: Garlic mashed potatoes in polymer packages processed in a microwave-assisted thermal sterilization (MATS) system had better retention of vitamin C compared to samples packaged in aluminum laminated pouches and processed in retort. Polymer packages combined with MATS processing could potentially provide safe, better quality, and nutritious shelf-stable food products for military and space missions.

Understanding water activity change in oil with temperature

Our recent studies and several publications suggest that the low water activity (a_w) of oil in thermal processing might be a major contributing factor towards the increased thermal resistance of bacteria in oils. In this study, we developed a reliable method to measure the water activity of oil by measuring the equilibrium relative humidity in a small headspace. Using this method, water activity of peanut oil was found to decrease exponentially with increasing temperature. A model derived from excess Gibbs free energy was fitted to the observations with an R² = 99.6% and RMSE = 0.01 (a_w). Our results suggest that the sharply reduced water activity of oil resulting from a rise in temperature could cause desiccation of bacteria. This is a possible explanation for the protective effect of oil in thermal processing.

•

A method is presented for the measurement of water activity of oil at temperatures up to 85 °C.

•

The water activity of peanut oil is found to decrease exponentially as the temperature increases.

•

A model is derived to predict the water activity of oil as a function of temperature.

•

Desiccation may happen to bacteria in oil during thermal processing, which explains the protective effect of oil.

The potential for microwave technology and the ideal profile method to aid in salt reduction

This study was the first to evaluate the influence of the combination strategies of flavor addition and microwave-assisted thermal sterilization (MATS) processing for salt reduction implications. In freshly prepared mashed potatoes, a 30% and 50% salt reduction (w/w) in comparison to a 100% salt sample with three flavor variations (no additional flavor, garlic, and pepper) were investigated. Also, using the ideal profile method (IPM), the influence of MATS versus retort processing, in comparison to a freshly prepared sample, and flavor addition on mashed potato sensory properties and acceptance was investigated. Chemical characterization using the electronic tongue for nonvolatile compounds and headspace solid-phase microextraction (HS-SPME)/gas chromatography-mass spectrometry (GC-MS) for volatile analysis was completed. IPM revealed the ideal data were consistent at both the panel and consumer levels from a sensory and hedonic perspective. Results demonstrated the ideal mashed potato product would remain low in bitterness but have more intense pepper and potato aromas and flavors than the current samples evaluated. The salt level could be reduced by 50% while still maintaining flavor and overall acceptance in freshly prepared samples, but this was accompanied by a loss in saltiness intensity perception. The saltiness intensity was not different from the freshly prepared samples when processed via MATS but was different when processed by the retort. For chemical characterization, the electronic tongue showed a high discrimination index (>89%) and correlated highly (>0.8) with many sensory attributes. As salt concentration in the mashed potatoes decreased, the recovery of volatile compounds decreased. The present work contributes to the understanding of product reformulation for the purpose of salt reduction. PRACTICAL APPLICATION: Product developers need strategies to bring salt down to target levels while maintaining consumer acceptance. The combination strategies of flavor addition and MATS processing may allow for a new strategy to assist product developers in reaching salt reduction targets. Furthermore, developers should bear in mind that noticeable intensity differences may not alter the preference for the product. Thus, intensity differences that result in changes in acceptance should be the focus of quality insurance rather than utilizing just noticeable differences.

Natural color pigments: oxidative stability and degradation kinetics during storage in thermally pasteurized vegetable purees

BACKGROUND

Package oxygen transmission rate (OTR) can affect the stability of natural color pigments such as anthocyanins, betalains and chlorophylls in foods during storage. In the present study, we investigated the oxygen sensitivity of selected pigments in thermally pasteurized vegetable purees held at a refrigeration temperature. We modulated the oxygen ingress in packaging using multilayer films with OTRs of 1, 30 and 81 cm3  m-2  day-1 . Red cabbage, beetroot and pea purees were vacuum packed, pasteurized to achieve a cumulative lethality ofP 90 ° C 10 ° C = 12.8-13.4 min and stored at 7 °C for 80 days.

RESULTS

Anthocyanins were relatively stable (< 4% losses), regardless of the film OTR. Betalains showed the highest sensitivity to different OTRs, with total losses varying from 4% to 49% at the end of storage and showing significant differences (P < 0.05) among the three films. Chlorophylls showed no significant difference (P > 0.05) in sensitivity to film OTRs. However, continuous degradation of chlorophylls was observed for all film types, with total chlorophyll losses ranging from 33% to 35%. Overall color differences (ΔE) at the end of storage for cabbage, beet and pea puree were between 0.50-1.70, 1.00-4.55 and 7.41-8.08, respectively. Betalains and chlorophylls degradation followed first-order and fractional conversion kinetics, whereas ΔE followed zero-order and fractional conversion kinetics during storage.

CONCLUSION

All three pigments behaved differently to oxygen ingress during storage. Low to medium barrier films are suitable for products containing red cabbage anthocyanins. High barrier films are must for betalains, whereas medium to high barrier films are suitable for chlorophyll-containing products. © 2019 Society of Chemical Industry.

Development of an Oxygen Sensitive Model Gel System to Detect Defects in Metal Oxide Coated Multilayer Polymeric Films

Metal oxide coated multilayered polymeric pouches provide a suitable alternative to foil-based packaging for shelf-stable products with extended shelf-life. The barrier performance of these films depends upon the integrity of the metal oxide coating which can develop defects as a result of thermal processing and improper handling. In this work, we developed a methodology to visually identify these defects using an oxygen-sensitive model gel system. Four pouches with different metal oxide coatings: MOA (Coated PET), MOB (SiO_x -coated PET), MOC (Overlayer-AlO_x -Organic-coated PET), MOD (Overlayer-SiO_x -coated PET) were filled with water and retort-processed for 30 and 40 min at 121 °C. After processing, the pouches were cut open, dried and subsequently filled with a gel containing methylene blue that changes color in the presence of oxygen. The pouches were then stored at 23 and 40 °C for 180 and 90 days, respectively. Defects were identified by observing the localized color change from yellow to blue in the packaged gel. These observations were confirmed through measurement of oxygen and water vapor transmission rates, as well as SEM and CLSM analyses. The MOC pouches showed the least change in barrier properties after thermal processing. This was due to crosslinking in the organic coating and protection provided by the overlayer. The melting enthalpy of all films increased significantly (P < 0.05) after sterilization. This may increase the brittleness of the substrates after processing. Findings may be used to improve the barrier performance of metal oxide coated polymeric films intended for food packaging applications. PRACTICAL APPLICATION: In this study, we developed a methylene blue-based, oxygen-sensitive model gel system to identify defects in metal oxide coated polymeric structures induced by thermal processing and mechanical stresses. We also performed a comprehensive analysis of these defects through CLSM and SEM. The gel system and methodology developed may be useful in the design and development of high barrier metal oxide coated films.

Utilizing Herbs and Microwave-Assisted Thermal Sterilization to Enhance Saltiness Perception in a Chicken Pasta Meal

This study was the first to evaluate the influence of herb addition in a complex food matrix processed by microwave-assisted thermal sterilization (MATS) system for potential salt reduction implications. In a chicken pasta meal, salt concentrations included 100% (full salt) and reduced salt variations (75%, 50%, and 25% of the original salt concentration) and for each meal, a version with and without herb addition. The influence of storage time on sensory perception and acceptance was investigated, along with the odor-induced saltiness enhancement (OISE). Trained sensory panel results showed that the addition of herbs to the chicken pasta meal increased the intensity of many flavors and led to an increased saltiness perception, demonstrating their congruency with salty taste. The addition of herbs allowed for a 50% salt reduction in a processed prepared meal while maintaining the same intensity of saltiness perception as determined by a trained panel and overall meal acceptance by consumers. The OISE was only significant for the 25% salt meal (P < 0.05) suggesting that the influence of herb addition on saltiness perception at lower salt concentrations was more influential than at higher salt concentrations. Over longer storage times, meals processed by MATS and stored at ambient temperature increased in aroma, taste, and flavor intensities as well as in acceptance of many meal attributes. This study contributed an additional strategy of product reformulation, specifically herb addition, to the portfolio of salt-reduction strategies for prepared meals using MATS. PRACTICAL APPLICATION: The addition of herbs to prepared meals (chicken pasta) may allow for up to a 50% reduction in salt content while maintaining the same saltiness intensity perception and overall consumer acceptance. This has important implications for the food industry as sodium reduction is a complex task. Furthermore, the additional herbs utilized in this study increased the intensity of certain aromas and flavors, and led to increased saltiness perception; these herbs could be considered in future salt reduction applications as this study demonstrates their congruency with salty taste.

A Fluorescence-based Method for Estimation of Oxygen Barrier Properties of Microspheres

In this study, we developed a fluorescence method to quantify oxygen barrier properties for wall materials used in microencapsulation of oxygen-sensitive compounds. We used a reversible, oxygen quenching dye, tris (4,7-diphenyl-1, 10-phenanthroline) ruthenium(II) dichloride complex, as a marker to monitor oxygen transport across spray-dried and freeze-dried Hi-cap100 and maltodextrin microspheres. We fit the rate of oxygen transport to Fick's second law and extrapolated an effective oxygen diffusion coefficient Deff. Results show that the Deff for spray-dried maltodextrin and Hi-cap100 formulations were in the range of 6.46 × 10^-15 to 7.45 × 10^-15  m² /s and 16.0 × 10^-15 to 22.4 × 10^-15 m² /s, respectively. Results also show an increasing trend in thiobarbituric acid reactive substances reaction rate constants, with an increasing D_eff for each formulation. Additionally, freeze-dried maltodextrin formulations had significantly higher D_eff (31.1 × 10^-15 to 36.0 × 10^-15 m² /s) compared to spray-dried matrices due to a more porous morphology. This new method provides a framework for the in situ estimation of D_eff for wall materials in microspheres. Potential applications include the design and selection of wall materials for maximum oxidative stability of encapsulated ingredients. PRACTICAL APPLICATION: Currently, the selection of wall materials used in microencapsulation of lipids takes a trial-and-error approach, which can be time consuming and prone to error. In this study, we developed a new methodology to directly assess the oxygen barrier properties of wall materials in microspheres. This method can be used by food scientists to screen wall materials in order to optimize the oxidative stability of encapsulated lipids.

Vacuum impregnation of firming agents in red raspberries

BACKGROUND

Red raspberries are a delicate and highly perishable fruit with a fragile pulp tissue. In this study we used vacuum impregnation (VI) methods to incorporate pectin and calcium chloride into whole red raspberries to improve their firmness. Specifically, we impregnated low methoxyl pectin (LMP) at 10 g of pectin kg^-1 of solution and calcium chloride (CaCl₂ ·2H₂ O) at 30 g calcium kg^-1 of pectin, and on the other side pectin methylesterase (PME) at 10 g of enzyme kg^-1 of solution, and (CaCl₂ ·2H₂ O) at 10 g of calcium kg^-1 of solution, into whole red raspberries. We tested three vacuum levels 33.9, 50.8, and 67.8 kPa, three vacuum impregnation times 2, 7, and 15 min, and two temperatures, 20 and 40 °C, during VI treatment. Maximum force (F_M ) and gradient (G_C3 ) were evaluated to assess raspberry firmness.

RESULTS

A vacuum level of 50.8 kPa, processing time of 7 min, and a LMP and calcium infusion at 20 °C resulted in the firmest fruit compared to the other treatments. At these VI treatment conditions, F_M and G_C3 values of red raspberries obtained were 28 N, and 8.4 N mm^-1 , respectively.

CONCLUSION

The optimal VI conditions identified in this study can be used to improve firmness and structural integrity of red raspberries by infusion of LMP and calcium. Findings on vacuum-impregnated red raspberries may be used to develop dehydrofrozen berries for incorporation into bakery and dairy products. © 2018 Society of Chemical Industry.

Monitoring Shelf Life of Pasteurized Whole Milk Under Refrigerated Storage Conditions: Predictive Models for Quality Loss

The shelf life of pasteurized milk is generally determined through microbiological analysis. The objective of this study was to correlate microbial quality parameters then to design predictive models for shelf life of pasteurized milk. We analyzed pasteurized milk (3.9% fat) for aerobic plate counts (APCs), psychrotrophic bacteria counts (PBCs), and Bacillus spp. counts at 5, 7, 10, 13, 15, and 19 (±1 °C) to the end of storage time. We also monitored titratable acidity, pH, and, lipase, and protease activity and correlated this with APC, which is the principal index defining shelf life. Results indicate that the shelf life of pasteurized milk was 24, 36, and 72 h at 19, 15, and 13 °C respectively, as determined by APC and acidity indicators. However, milk stored at lower temperatures of 5, 7, and 10 °C had longer shelf life of 30, 24, and 12 d, respectively. A sharp increase in titratable acidity, while decrease pH were observed when APCs reached 5.0 log₁₀ CFU/mL at all storage temperatures. Lipase and protease activities increased with storage temperature. At 5 and 7 °C, however, protease activity was very low. Therefore, we eliminated this parameter from our quality parameters as a potential spoilage indicator.

PRACTICAL APPLICATION

Findings of this research are useful for monitoring the quality of commercial pasteurized milk, particularly in locations where environmental conditions make longer storage difficult. The study also provides valuable information for development of colorimetric shelf life indicators.

Green Pea and Garlic Puree Model Food Development for Thermal Pasteurization Process Quality Evaluation

Development and selection of model foods is a critical part of microwave thermal process development, simulation validation, and optimization. Previously developed model foods for pasteurization process evaluation utilized Maillard reaction products as the time-temperature integrators, which resulted in similar temperature sensitivity among the models. The aim of this research was to develop additional model foods based on different time-temperature integrators, determine their dielectric properties and color change kinetics, and validate the optimal model food in hot water and microwave-assisted pasteurization processes. Color, quantified using a* value, was selected as the time-temperature indicator for green pea and garlic puree model foods. Results showed 915 MHz microwaves had a greater penetration depth into the green pea model food than the garlic. a* value reaction rates for the green pea model were approximately 4 times slower than in the garlic model food; slower reaction rates were preferred for the application of model food in this study, that is quality evaluation for a target process of 90 °C for 10 min at the cold spot. Pasteurization validation used the green pea model food and results showed that there were quantifiable differences between the color of the unheated control, hot water pasteurization, and microwave-assisted thermal pasteurization system. Both model foods developed in this research could be utilized for quality assessment and optimization of various thermal pasteurization processes.