Recent advances in pressure modification-based preservation technologies applied to fresh fruits and vegetables

Investigation of crystal growth of CO2 hydrate in aqueous fructose solution for the potential application in carbonated solid foods

CO₂ hydrate is applicable to solid carbonated foods. The hydrate crystal morphology, which represents the crystal size and shape, is an important characteristic that changes the texture of foods. We report an observational study of the crystal growth of CO₂ hydrate in aqueous fructose solution. The difference between the phase equilibrium temperature and the experimental temperature, ΔT_sub, is applied as an index of the driving force. Experiments were performed at ΔT_sub range of 0.9 K to 5.4 K. At all ΔT_sub, initial crystal formed at the gas-solution interface and grew along the interface. After covering the interface, the crystals grew in the liquid phase The individual crystals were identified as polyhedral with facets (ΔT_sub = 0.9 K), skeletal crystals (ΔT_sub = 2.0 K) and dendrites (ΔT_sub = 3.0 K and 5.4 K). Based on these results, the potential effect of gas hydrate morphology on texture of foods has been discussed.

Light-emitting diodes (below 700 nm): Improving the preservation of fresh foods during postharvest handling, storage, and transportation

In order to maintain the original taste, flavors, and appearance, fresh foods usually do not go through complex processing prior to sale; this makes them prone to deterioration due to external factors. Light-emitting diodes (LEDs) have many unique advantages over traditional preservation technologies leading to their increasing application in the food industry. This paper reviews the luminescence principles of LED, the advantages of LED compared with traditional lighting equipment, and its possible preservation mechanism, and then critically summarizes the beneficial effects of LED irradiation on the ripening and aging process of various fruits and vegetables (climacteric and non-climacteric). The activity changes of many enzymes closely related to crop development and quality maintenance, and the variation of flavor components caused by LED irradiation are discussed. LED illumination with a specific spectrum also has the important effect of maintaining the original color and flavor of meat, seafood, and dairy products. For microorganisms attached to the surface of animal-derived food, both 400-460 nm LED irradiation based on photodynamic inactivation principle and UV-LED irradiation based on ultraviolet sterilization principle have high bactericidal efficacy. Although there is still a lack of useful standards for matching optimal LED irradiation dose with wavelength, perhaps in the near future, the improved LED irradiation system will be applied extensively in the food industry.

Effect of Low Pressure and Low Oxygen Treatments on Fruit Quality and the In Vivo Growth of Penicillium digitatum and Penicillium italicum in Oranges

Penicillium digitatum and P. italicum are the major postharvest pathogens in citrus. To reduce postharvest decay, the use of low-oxygen (0.9 kPa O2) (LO) or low-pressure (6.6 kPa) (LP) treatments were evaluated during the storage of navel oranges for four or eight days. The results showed that exposure to both LO and LP treatments reduced in vivo pathogen growth compared to the untreated (UTC) oranges, with LO being the most effective. The effects of LO and LP on fruit metabolism and quality were further assessed, and it was found that there was no effect on fruit ethylene production, respiration rate, TSS (total soluble solids), TA (titratable acidity) or fruit firmness. However, both LO and LP treatments did have an effect on juice ethanol concentration and fruit weight-loss. The effect of adding exogenous ethylene at either LP (1 µL/L) or atmospheric pressure (AP) (at either 0.1, 1 µL/L) was also evaluated, and results showed that the addition of ethylene at these concentrations had no effect on mould diameter at LP or AP. Therefore, both LO of 0.9 kPa O2 and LP of 6.6 kPa at 20 °C are potential non-chemical postharvest treatments to reduce mould development during storage with minimal effects on fruit quality.

Impact of selected baking and vacuum cooling parameters on the quality of toast bread

Vacuum cooling of baked goods can deliver many advantages in terms of product quality and productivity, such as higher volumes and shorter cooling times. However, the associated high costs and the need to adjust baking protocols are of relevance and more information is needed. This paper examines the influence of two main baking protocol parameters on the quality of toast bread, i.e. oven temperature and baking time reduction. Resulting toast bread characteristics including specific bread volume, concavity, browning index, crust and crumb hardness and a_w-value were analysed as well as process-dependent core temperature and water loss. In order to compensate for water loss during vacuum cooling and still achieve optimal toast bread quality, a final bread core temperature of 98 °C at the end of baking gave best results, regardless of oven temperature. It was further shown that cooling time can be reduced by a factor of 10 if the baking protocol is optimally adjusted, hinting at a huge potential to increase productivity for industrial applications. In summary, it can be stated that vacuum cooling requires a tailored reduction in baking time in order to compensate for water loss from vacuum cooling while retaining sufficient structural cohesion to resist deformation of the bread.

Hypobaric Packaging Prolongs the Shelf Life of Refrigerated Black Truffles (Tuber melanosporum)

Black truffle (Tuber melanosporum Vitt.) is a fine agro-food product known for its unique aroma and very limited shelf life (maximum of 5-7 days, room temperature). Hypobaric packaging at 30 kPa, a mix of 1% O₂/99% N₂, and 40% CO₂/60% N₂ were studied to prolong the shelf life of black truffle at 4 °C in sealed polypropylene vessels, compared to normal atmosphere. Epiphytic microbial population, firmness, weight loss, CO₂ formation, and sensory properties were monitored weekly up to 35 days of storage and were related to the volatile profile. Principal components analysis revealed good correlation between the storage time and the decrease of firmness, and the increase of the microbial count and CO₂ production. Only truffles stored under hypobaric conditions showed an acceptable quality after 14 days storage. Hypobaric packaging is a cheap strategy to prevent the swelling of vessels caused by respiration and can reduce the deviation from the high-quality level of the fresh product from one to at least two weeks.

Evaluation of Low Pressure and Vapor Heat as a Phytosanitary Treatment For Chlorophorus annularis (Coleoptera: Cerambycidae) in Postharvest Bamboo Poles

The bamboo longhorned beetle, Chlorophorus annularis (Fabricius), distributed widely in Asian countries attacking live or postharvest bamboo, is a concern to the international trade of bamboo materials. With the phase out of methyl bromide for quarantine and preshipment use, a reliable, safe, and environmentally friendly phytosanitary treatment is needed as an alternative. In this study, the thermotolerance of C. annularis larvae at atmospheric pressure was examined. The results showed that the thermotolerance increased with instar. The fifth instar was the most thermotolerant stage at 48 and 50°C. A series of vapor heat treatment tests were conducted for bamboo poles infested with C. annularis at the vacuum levels of 15, 30, 50, 70, 90, and 100 kPa at the temperatures of 40, 44, 48, 52, and 56°C with a holding duration of 15 min. The lower pressure or higher temperature increased the mortality of C. annularis. In total 473 larvae were treated at 48°C and 50 kPa for 15 min. Only one larva was found alive, resulting in a mortality rate of 99.7886%. In total 418 larvae were treated at 52°C and 100 kPa for 15 min resulting in 100% mortality. Based on these two results, a heat treatment of 52°C for 15 min at 50 kPa can be used as a low pressure vapor heat treatment for bamboo articles infested with C. annularis. The vapor heat treatment combined with low pressure is an effective alternative phytosanitary measure for bamboo articles.