Deepti Salvi

Effect of temperature abuse on frozen army rations. Part 1: Developing a heat transfer numerical model based on thermo-physical properties of food

Numerical simulation was carried out to predict the effect of external temperature conditions on thermal behavior of frozen US military rations, during storage and transportation. An army breakfast menu box containing beefsteaks, concentrated orange juice, peppers & onions, French toast, and Danishes, was selected for conducting this study. Thermo-physical properties of each food item were characterized using their composition and differential scanning calorimeter (DSC). Apparent heat capacity method was used to account for the latent heat of phase change during simulation of thawing and freezing. Numerically simulated results were experimentally validated using a gel-based model food system and the food items in the menu box. The average deviation between numerically predicted temperature and experimentally measured temperature for the model food system was approximately 1°C and for the targeted food items the deviation ranged from 2°C to 5°C, depending on the food item.

Effect of surface roughness in model and fresh fruit systems on microbial inactivation efficacy of cold atmospheric pressure plasma

This study investigates the efficacy of cold atmospheric pressure plasma (CAPP) on microbial inactivation as influenced by surface roughness of two types of surfaces: sandpaper and fresh fruit peel. Different grits of closed-coat sandpaper were selected, with their roughness (Pq) values ranging from 6 to 16 μm. Apple, orange, and cantaloupe peels were selected for roughness values that were similar to the sandpapers. The sandpapers and the fruit peel surfaces were spot inoculated with Enterobacter aerogenes (109 CFU/63.64 cm2) and exposed to CAPP for 492 s. Similar microbial enumeration techniques were used for both systems to quantify the microbial inactivation. The smoothest sandpaper showed a 0.52-log higher inactivation of E. aerogenes (2.08 log CFU/63.64 cm2 sandpaper surface inactivation) than did the roughest sandpaper (1.56 log CFU/63.64 cm2 sandpaper surface inactivation), and the difference was statistically significant (P < 0.05). The smoothest fresh fruit peel surface (apple) showed a 1.25-log higher inactivation of the microorganism (1.86 log CFU/63.64 cm2 fruit peel surface inactivation) than did the roughest fresh fruit peel surface (cantaloupe; 0.61 log CFU/63.64 cm2 fruit peel surface inactivation), and the difference was statistically significant (P < 0.05). As the surface roughness increased, microbial inactivation efficacy of CAPP decreased for both systems. The results from sandpaper show that, in a scenario in which the surface roughness was the only parameter of difference, the microbial inactivation efficacy of CAPP decreased with increasing surface roughness. The results from fruit surfaces show high variability and were not directly predictable from the sandpaper data. This suggests that the microbial inactivation efficacy of CAPP in real-world food systems, such as on fresh fruit peels, is affected by factors in addition to surface roughness.

Characterization of Microbial Inactivation Using Plasma-Activated Water and Plasma-Activated Acidified Buffer

This work investigates the efficacy of plasma-activated water (PAW) and plasma-activated acidified buffer (PAAB) on Enterobacter aerogenes in aqueous system and fruit systems. Reactive oxygen and nitrogen species in PAW have been suggested to provide antimicrobial and acidifying effects, causing the pH of treated water to drop. To isolate the effect of pH in microbial inactivation and to study the interactive effects of pH and reactive species on microbial inactivation, a citrate-phosphate buffer (pH 3.1) and PAAB (citrate-phosphate) were studied. A 1.92 ± 0.70 log CFU/mL reduction in E. aerogenes was observed in PAW, while no reduction was achieved in the buffer, suggesting that the inactivation was due to the reactive species in PAW and not the acidic pH. PAAB achieved a 5.11 ± 0.63 log CFU/mL reduction, suggesting an interactive effect of reactive species and low pH. Electrical conductivity and oxidation-reduction potential measurements suggest potential mechanisms for the greater antimicrobial efficacy of PAAB over PAW. Four surfaces of increasing roughness (glass slides, grape tomatoes, limes, and spiny gourds) were spot inoculated and washed with distilled water, PAW, buffer, and PAAB for 3 min. The smoothest surface (glass) showed the highest reduction (6.32 ± 0.43 log CFU per surface), while the roughest surface (spiny gourd) showed a significantly lower reduction (2.52 ± 0.46 log CFU per surface) when treated with PAAB. For treatment with PAW, no significant differences were observed between glass slides, limes, and spiny gourds. With PAW treatment, significantly lower reduction was observed on spiny gourds (1.70 ± 0.21 log CFU per surface) than on grape tomatoes (4.65 ± 1.34 log CFU per surface). PAW and PAAB both showed potential for their use in fresh produce sanitation.

High Pressure–Assisted Infusion in Foods

High pressure processing (HPP) has been greatly explored as a food preservation method over the past few decades but limited research is available on the use of HPP as a mass transport technique to infuse biomolecules into food matrices. The high pressures employed during HPP cause permeabilization of the cell structure of foods resulting in enhanced mass transfer rates of molecules in and out of the food matrix. Higher mass transfer rates can be achieved when HPP is used as a pretreatment prior to conventional infusion techniques. Simultaneous HPP infusion wherein infusion occurs under high pressure has been shown to increase both the rate and the amount of infusion. The amount of quercetin in cranberries subjected to HPP was 3–5 times higher and the infusion rate was 144 times faster compared to infusion at atmospheric pressure. The latest research is showing that pressure-driven transport and concentration-driven diffusion with concomitant cell permeabilization contribute to HPP infusion. The enhanced infusion achieved through HPP makes it a promising technology for manufacturing convenient, healthy, and nutritionally enhanced foods with a possibility of novel sensory appeal.

High Pressure Cold Pasteurization

High pressure processing (HPP) has been demonstrated to be an effective inactivation technique for a variety of pathogenic microorganisms, spoilage microorganisms, yeasts, molds, as well as quality-deteriorating enzymes. The microbial inactivation during HPP is mainly caused by an alteration in cellular morphology and inhibition of cell division under pressure. The high pressures used in HPP have little to no effect on the covalent bonds in the foods; hence HPP retains the original quality of food products in terms of micronutrients, color, flavor, and aroma while extending its microbial shelf life. Since HPP was first applied to foods in 1899, it has become a commercial technology in food industry over the last three decades. It has been approved as a cold pasteurization technique by the United States and other regulatory agencies for a limited number of pressure–time combinations for 6-log reduction of key food pathogens in acid foods held at room temperature and in low-acid refrigerated foods. Vegetable and fruit products such as juices, salsa, dressing and guacamole; meat products such as ready-to-eat deli meats and poultry; and seafood such as shellfish and fish products, are some of the commercially available HPP food products in the United States. HPP is proving to be an excellent cold pasteurization technique that causes effective inactivation of target spoilage and pathogenic microorganisms near room temperature, without significantly altering the nutritional and sensory qualities.

Effect of temperature abuse on frozen army rations. Part 2: Predicting microbial spoilage

Numerically simulated heat transfer model of frozen US military rations was combined with microbial kinetics to predict the microbial spoilage of the food products, during two possible temperature abuse scenarios. An army breakfast menu box containing five different food items was selected for conducting this research. One of the food item in the menu box, beefsteak, was chosen for detailed microbial study. A microbial predictive tool was used to identify and evaluate the kinetics of the most prone microorganism that can grow in a beefsteak. Numerical predictions suggested that the food items exposed to external temperatures ranging from 20°C to 40°C can be allowed to stay at those temperatures for maximum times of 28.7h to 11.9h, respectively. The food items can be allowed to stay inside the broken freezer for a maximum time of 186h, to ensure microbial safety in the case of freezer failure.