Growth and development of Tunisia soft seed pomegranate and its quality formation regulation

Abstract: 【Objective】Tunisia soft seed pomegranate has developed into one of the main industries in Xinyang, Henan province, and has been introduced to other areas in China. With the development of Tunisia soft seed pomegranate industry, many problems encountered in the production restrict its sustain-able development. One of the main problems is that there is an ambigious standard on harvesting maturi-ty. Some fruits are harvested early according to the market demand, which undermines the expectation of this cultivar of consumers. Some fruits are harvested late based on their appearance and aril color which results in poor storage property. Fruit is harvested with no maturity guide, resulting in large dif-ferences in quality, which causes confusion in marketing. The objective of this research is to study the quality development and its regulation in fruit of Tunisia soft seed pomegranate and analyse the correla-tions among quality indicators during fruit development. The results will provide guidance of maturity for harvest and to provide reference for cultivation management in order to improve fruit quality.【Meth-ods】The tubular flowers (hermaphrodite flowers with well-developing pistil) with the same flowering period were selected and labeled, and the longitudinal and transverse diameters of the fruit from the labeled flowers were measured in field at regular intervals. Samples were taken back to the laboratory im- mediately to measure their quality indexes, such as average weight, specific weight, rate of aril to fruit, 100-aril weight, soluble solid content (SSC), titratable acid (TA), pH, L, a and b values, anthocyanins,and their aril sensory quality. The principal component and correlation analysis were then performed.【Results】During fruit development of Tunisia soft seed pomegranate, the longitudinal and transverse di-ameters both showed a double S trend, and the growth of the transverse diameter was much greater than that of longitudinal diameter (up to 25%). The fruit shape index displayed a downward trend and de-creased to 0.89 when fruit were ripe. The average fruit weight experienced three rapid growth periods,and fruit weight on 123 DAFB had no significant difference from the maximum weight. During fruit de-velopment, the increasing patterns of weight and volume were similar, but the former laged behind the latter. At immature stage, the aril weight increased more rapidly than that of the other parts such as peri-carp. At the middle and late growth stages, the weight of uneatable parts such as pericarp increased more rapidly than that of the aril. Therefore, the rate of aril to fruit of Tunisia soft seed pomegranate at ripe was significantly lower than the maximum during the development. The 100-aril weight showed an overall upward trend, increased significantly in the middle of July and in the middle of August, and reached the highest level (67.72 g) in the early October. SSC showed a double S rising trend, and reached 15.4% on 108 DAFB having no significant difference from the maximum value on 118 DAFB(16.0%). The content of TA showed a slow decreasing trend as a whole, and decreased rapidly between123 DAFB and 131 DAFB. The pH value rose significantly after 118 DAFB. The ratio of SSC to TA in-creased slowly before 123 DAFB, and then increased significantly in the later period, reaching 56.7 on 131 DAFB. The optimum aril quality was achieved on 98 DAFB. The a value of the peel increased sig-nificantly from 108 DAFB to 118 DAFB, and the rapid increase in the peel occurred about 10 days later than that in the aril. In the aril, the a value was basically in line with anthocyanin content. The content of anthocyanins in the aril showed a double S trend, with the maximum daily increase (10.9%) occur-ring from 118 DAFB to 123 DAFB. The L value decreased with aril coloring, especially from 108 DAFB to 131 DAFB, hence, the L value of the aril may be a reliable index to judge fruit maturity. Fruit weight, L value of the peel, SSC and a value of the aril color could be used as the main factors for quali-ty evaluation. There was a significant positive correlation among all the main factors except the L value of the peel. And between the main factors and a value of the peel and the content of anthocyanin in ar-ils, the correlation was significantly positive, while L value of the aril was significantly and negatively correlated with the main factors.【Conclusion】Tunisian soft seed pomegranate fruit in Xingyang, Henan province, has a double S trend in weight and size. The comprehensive quality is formed cheifly from 108 DAFB to 118 DAFB. On 118 DAFB, the fruit displayed the basic properties of the cultivar. After 118 DAFB, the aril color and SSC/TA increased rapidly and the L value decreased significantly. During fruit development of Tunisia soft seed pomegranate, weight, SSC, L value of the peel and a value of the aril can be used as the main factors for quality evaluation. Combined with SSC, L value of the peel and a value of the aril (main factors of quality evaluation), L value of the aril and pH can be used as reliable indicators for judging maturity. The rapid development of fruit longitudinal and transverse diameters can partially explain fruit cracking in different periods, which may provide some guideline for prevent-ing fruit cracking. The TA and L values of Tunisia soft seed pomegranate aril decreases rapidly during fruit ripening. Therefore, the harvest maturity has a great influence on the postharvest quality and stor-ability.