Effect of Heat Treatment on the Quality and Soft Rot Resistance of Sweet Potato during Long-Term Storage

Heat treatment is a widely applied technique in the preservation of fruits and vegetables, effectively addressing issues such as disease management, rot prevention, and browning. In this study, we investigated the impact of heat treatment at 35 °C for 24 h on the quality characteristics and disease resistance of two sweet potato varieties, P32/P (Ipomoea batatas (L.) Lam. cv 'Pushu13') and Xinxiang (Ipomoea batatas (L.) Lam. cv 'Xinxiang'). The growth in vitro and reproduction of Rhizopus stolonifer were significantly inhibited at 35 °C. However, it resumed when returned to suitable growth conditions. The heat treatment (at 35 °C for 24 h) was found to mitigate nutrient loss during storage while enhancing the structural characteristics and free radical scavenging capacity of sweet potato. Additionally, it led to increased enzyme activities for APX, PPO, and POD, alongside decreased activities for Cx and PG, thereby enhancing the disease resistance of sweet potato against soft rot. As a result, the heat treatment provided a theoretical basis for the prevention of sweet potato soft rot and had guiding significance for improving the resistance against sweet potato soft rot.

Distinct Tomato Cultivars Are Characterized by a Differential Pattern of Biochemical Responses to Drought Stress

Future climate scenarios suggest that crop plants will experience environmental changes capable of affecting their productivity. Among the most harmful environmental stresses is drought, defined as a total or partial lack of water availability. It is essential to study and understand both the damage caused by drought on crop plants and the mechanisms implemented to tolerate the stress. In this study, we focused on four cultivars of tomato, an economically important crop in the Mediterranean basin. We investigated the biochemical mechanisms of plant defense against drought by focusing on proteins specifically involved in this stress, such as osmotin, dehydrin, and aquaporin, and on proteins involved in the general stress response, such as HSP70 and cyclophilins. Since sugars are also known to act as osmoprotectants in plant cells, proteins involved in sugar metabolism (such as RuBisCO and sucrose synthase) were also analyzed. The results show crucial differences in biochemical behavior among the selected cultivars and highlight that the most tolerant tomato cultivars adopt quite specific biochemical strategies such as different accumulations of aquaporins and osmotins. The data set also suggests that RuBisCO isoforms and aquaporins can be used as markers of tolerance/susceptibility to drought stress and be used to select tomato cultivars within breeding programs.

Comparison of different analytical methods to evaluate the heat shock protein (HSP) response in fruits. Application to tomatoes subjected to stress treatments

Heat shock proteins (HSP) are synthesized in living tissues exposed to transient increase in temperature and play a central role in the protective response against heat and other stresses. In fruits, this response to heat treatment provides resistance to a physiological alteration known as chilling injury. Despite the physiological importance of this group of proteins, publications comparing different methodological alternatives for their analysis are rather scarce. In the present paper, we conducted a comparative study using different electrophoretic and immunological techniques to evaluate the HSP response in fruits. Proteins were extracted from tomato fruit exposed to an HSP-inducing temperature (38 °C) for different times (0, 3, 20, and 27 h). Different alternatives of analysis (SDS-PAGE, SDS-PAGE followed by IEF, Western blot, and dot blot) were performed, and their potential application discussed. The study was complemented with a practical application, in which tomatoes were subjected to heat and anaerobic treatments and then stored in a chill-inducing temperature. This application evidences the relevance of knowing the level of proteins attained by stress treatments which correlates with the acquired tolerance.

•

HSP evaluation can be used for practical purposes.

•

To assess the HSP response in fruits, different complementary methods should be used.

•

A simple method (dot blot) can quantify HSP induced in fruits by heat exposure.

•

HSP level induced by stress treatments correlates with acquired physiological tolerance.

Effect of infield handling conditions and time to pre-cooling on the shelf-life and quality of tomatoes

Abstract This study investigates the effects of post-harvest handling practices prior to storage on the quality of tomatoes in South African supply chains. Pink mature tomatoes were harvested in the morning and afternoon, transported from two farms located 40 km apart to two central pack houses located near each of the farms in Limpopo, South Africa. The samples were transported using bins (468 kg capacity) and lugs (20 kg capacity). After harvesting, the samples were either immediately transported to the pack house and precooled within two hours, or left in the field and transported to the pack house to be pre-cooled after six hours, to simulate delays during transportation. On arrival at the pack houses, the fruit was sampled from the bottom 0.15 m of each lug or bin, precooled using forced air and washed. After precooling, the samples were stored either under ambient conditions or refrigerated storage (15±2 °C). The tomato colour, firmness, weight loss, marketability and pH were monitored over a 24-day storage period. The rate of change of the fruit hue angle was significantly (p ≤ 0.05) higher for samples handled using bins as compared to those handled using lugs. Handling conditions had no significant (p > 0.05) effect on the rate of loss of fruit flesh firmness. The bottom layer of fruit stored in bins showed 30% mechanical damage as compared to 2% in lugs. Harvesting in the morning and pre-cooling within two hours improved fruit marketability and weight-loss by up to 200 kg/ton and 75 kg/ton, respectively, as compared to harvesting in the afternoon and pre-cooling after six hours. As the best practices for industry, the study recommends minimizing the time to pre-cooling, harvesting in the morning and using lugs to handle the fresh tomatoes.