Reducing postharvest losses in persimmon. Pre and postharvest aspects involved in fruit quality and new strategies for valorization

Persimmon is a crop of great relevance in Spain, which has become the world’s second producer and the largest exporter. This production centers mainly on cv. Rojo Brillante in the Valencian Community. In recent years however, Spain has experienced overproduction, which has led to important economic losses and increased fruit waste. Moreover, different preharvest factors, which affect fruit quality, and an inadequate postharvest management, can lead to important postharvest losses. In this context, the objective of the present Thesis is to study strategies to increase persimmon crop profitability by reducing postharvest losses and revalorizing discarded fruit and surplus production. For this purpose, the pre- and postharvest aspects involved in persimmon fruit quality are discussed. Besides, whole fruit drying is proposed as a new valorization strategy. Of the preharvest aspects related to fruit quality parameters, the plant nutritional status is a major factor that can affect plant material composition and fruit characteristics. Thus, Chapters I and II addressed the study of macro- and micronutrients concentrations in the leaves and fruit from organic and conventional management systems, and their relation to the main fruit quality parameters in ‘Rojo Brillante’ persimmon. The main biocomponents in the fruit from both crop systems were also evaluated. The greater macro- and microelements supplied in the conventional vs. the organic system did not imply a higher accumulation of these elements in leaves and fruit. Macroelements concentration in fruit depended on the fruit flesh area evaluated (apical or basal). The correlation between macronutrients and fruit quality parameters revealed that the Ca and Mg, and the N/Ca and Ca/(K+Mg) ratios were closely related to color, firmness, total soluble solids, and soluble tannins content. The influence of crop management on fruit biocomponents concentration was observed only for malic acid, β-Cryptoxanthin and ascorbic acid, which were higher in the organic than the conventional fruit. The greatest agronomic efficiency noted in the organic crop indicates that the lower fertilization rate in such management is adequate for obtaining fruit with optimal nutrient concentrations and reveals the important role of organic matter in favoring nutrient assimilation. The results obtained in this study provide new information about the nutritional composition of persimmon grown by organic and conventional management and reinforce the need for balanced fertilization to achieve good fruit quality. Another preharvest aspect to consider in persimmon management is the application of phytoregulators to prolong the harvesting season. For ‘Rojo Brillante’, ethephon use is normal to advance harvest, as is gibberellic acid (GA3) to delay maturation. These treatments can affect fruit quality at both harvest and postharvest. Therefore, the postharvest 1-methylcyclopropene (1-MCP) treatment is commonly applied to guarantee postharvest fruit quality. However, the pre-harvest 1-MCP application has been shown to be a novel effective treatment for other fruit types, but with very little information for persimmon. In Chapter III, the effect of this treatment was evaluated in different scenarios combined with ethephon or GA3. The results showed that preharvest 1-MCP extended the harvest window and prolonged the commercialization period when applied to the ethephon-treated fruit. In the GA3-treated fruit, which are to be cold-stored, the preharvest 1-MCP treatment can replace the 1-MCP postharvest application, which could be a useful tool for optimizing handling operations in packinghouses. For ‘Rojo Brillante’, an effect of harvest moment on fruit behavior during cold storage has been commercially documented. To explain these differences, in Chapter IV an in-depth physico-chemical and microstructural characterization of fruit (pretreated with GA3) during five commercial harvests (from November to December) is carried out. Moreover, the firmness changes during cold storage at 0 °C up to 90 days are evaluated. During the studied harvest period, fruit presented high firmness values, which are useful for fruit to be cold stored. Nevertheless, the minor differences revealed in persimmon firmness at harvest strongly influenced fruit behavior during cold storage. Accordingly, the fruit harvested in mid-November had the highest storage potential by maintaining firmness high for up to 90 days, which did not happen in the fruit from subsequent harvests. These differences in postharvest behavior were associated with structural parenchyma integrity at harvest. On the other hand, it is noteworthy that deastringency treatment is one of the main steps of postharvest handling associated with postharvest losses because it directly influences final fruit quality. Although high CO2 concentrations are the most commercially applied deastringency treatment, ethanol is also employed in some countries like Brazil. With ‘Giombo’ persimmon, one of the main cultivars in this country, complete astringency loss proves difficult. In this Thesis (Chapter V), the ‘Giombo’ persimmon treated with ethanol or CO2 to remove astringency is evaluated to know the physico-chemical and microstructural changes that occur during cold storage. The results suggested that, although ethanol is the usual deastringency treatment for ‘Giombo’, high CO2 concentrations are recommended to achieve the fastest tannins insolubilization and to maintain greater flesh firmness during cold storage. In order to valorize discarded persimmon fruit and surplus production, in this Thesis, whole fruit drying is proposed as a new strategy for ‘Rojo Brillante’. A first study (Chapter VI) approaches the physico-chemical and microstructural changes that occur during the natural-air drying of persimmon. The obtained results revealed that this variety is suitable for being subjected to the natural drying process by taking into account that the maturity stage influences final product characteristics. To improve the drying process, convective hot-air drying is also evaluated (Chapter VII). After evaluating drying at three temperatures (35 ᵒC, 40 ᵒC and 45 ᵒC), the results showed that the higher the drying temperature, the faster the drying process was, and the final product characteristics depended on the drying temperature, especially in texture terms. Drying at 35 ᵒC resulted in a product with similar physico-chemical attributes to those achieved by the natural drying method, but in a much shorter time, which improves the commercial viability of this treatment.