Mitigation of High Solar Irradiance and Heat Stress in Kiwifruit during Summer via the Use of Alleviating Products with Different Modes of Action—Part 2 Effects on Fruit Quality, Organoleptic, and Phytochemical Properties at Harvest and after Storage

In Greece, kiwifruit is grown in areas characterized by high temperatures during the summer months, with high solar radiation, especially during the period of shoot growth and fruit maturation. Therefore, the impact of heat stress is crucial. The objective of the present study was to evaluate the effect of pre-harvest alleviating products’ application in the field on the yield and fruit quality attributes of ‘Hayward’ kiwifruit before and after storage. To achieve this, the osmoprotectant BlueStim (glycine betaine), the reflectant Purshade (calcium carbonate 62.5% w / w ), and the antioxidant Sun Protect were applied by foliar spraying. Fruits produced under the influence of BlueStim exhibited high soluble sugars, total phenols, total flavanols, total flavonoids, and FRAP antioxidant capacity at harvest, while the production per vine increased by almost 17% compared to control. After storage, fruits produced from vines pre-harvest treated with BlueStim showed increased concentrations of soluble sugars, ascorbic acid, total organic acids, total flavonoids, and antioxidant capacity. Fruits produced from vines treated with Purshade presented high concentrations of soluble sugars, total phenols, FRAP and DPPH antioxidant capacity, total soluble solids, and malic acid, while Sun Protect application resulted in increased fruit firmness and total phenols as well. Therefore, the applied treatments alleviated, to some extent, the negative impact of heat stress on fruit quality, with variable effects on the measured quality parameters.