Optimal harvest date determination and its effect on storage quality in 'Huashuo' apples

Abstract: 【Objective】‘Huashuo'apple is an excellent early-season cultivar derived from the cross between hybrid‘NY543'and‘Huaguan'by Zhengzhou Fruit Research Institute. The‘Huashuo'fruits are large in size with bright color, sweet taste, pleasant flavor, and longer storage time and shelf life.Since the harvest period of‘Huashuo'apple fruits is in August when the weather is sunny and hot, the postharvest storage ability is very important for sake of the development of this cultivar. Among the various factors affecting postharvest quality of fruits, the harvest maturity is one of the most important preharvest factors. However, there have been no researches on the maturity determination and postharvest quality changes during storage for‘Huashuo'apples. The objective of this research is to explore the method for the harvest maturity identification of‘Huashuo'fruits and find out the optimal harvest date.【Methods】‘Huashuo'fruits picked at different harvest dates(harvest date Ⅰ, harvest date Ⅱ and harvest date Ⅲ) were stained with iodine to build the starch-iodine staining chart. In the meantime, other physico-chemical qualities including flesh firmness, seed firmness, soluble solid content(SSC), sugar/acid ratio, ethylene evolution rate, starch content and starch-iodine index of‘Huashuo'apples harvested at different maturities were investigated to study their differences and relationships. Besides, the storage properties of‘Huashuo'apples at different maturities were studied during cold storing at 1 ℃ for90 d and then 15 d shelf-life at room temperature. The modifications of fruit firmness, ethylene evolution rate, soluble sugar, titratable acid and starch contents were measured during the postharvest storage to find out the differences among different harvest maturities.【Results】Results showed that‘Huashuo'apples at harvest ripe stage could be classified into 8 levels according to the starch-iodine staining chart.In this research,‘Huashuo'apples of harvest date Ⅰ were at 1-2 levels with 20%-50% core staining and 100% flesh staining; those of harvest date Ⅱ were at 3-4 levels with 0% core staining and 60%-80% flesh staining; and those of date Ⅲ were at 5-6 levels with 20%-40% flesh staining. And the fruits at 7-8 levels were full-ripe, whose flesh was stained no more than 10% by iodine. Though the starch-iodine staining method was traditionally used to identify the maturity stages of apples, it could not predict exact harvest dates because it may be influenced by orchard factors that did not influence fruit maturity.So other quality characteristics related to maturity of‘Huashuo'apples were measured. The results showed seed firmness and SSC were significantly higher at later harvest date(Ⅲ) than harvest date Ⅰ,starch content was higher in apples harvested at date Ⅰand Ⅱ than date Ⅲ. For‘Huashuo'apples harvested at optimal date(Ⅱ), the fruit firmness and SSC showed no significant differences with harvest date Ⅲ. And there was no significant difference in seed firmness and starch content with apples from harvest date Ⅰ. Sugar/acid ratio, ethylene evolution rate and starch-iodine index were significantly different among these 3 harvest stages, which could be used as determining qualities of‘Huashuo'apple fruit harvest date and maturities. During postharvest storage and shelf life of‘Huashuo'apples, firmness, starch and titratable acid contents decreased, while the ethylene evolution rate and soluble sugar content increased. Earlier picked(harvest date Ⅰ)‘Huashuo'fruits possessed higher firmness, starch and titratable acid contents, and lower sugar content at harvest. The firmness declined faster during storage period and the soluble sugar content was significantly less than optimal harvested(harvest date Ⅱ)and later harvested(harvest date Ⅲ) fruits, which affected the fruit taste in shelf-life. For the later harvested apples, the ethylene evolution rate was significantly higher when fruits were stored after 42 d and in shelf life, as the fruit firmness decreased to the lowest after shelf life, which meant the shelf life would be shorten at this harvest maturity. Harvest date Ⅱ could be the optimum harvest period for‘Huashuo'apples, as their sugar/acid ratio was medium with great taste at harvest. In the meantime,the storage qualities including flesh firmness, soluble sugar and titratable acid contents were higher than other harvest dates.【Conclusion】The effective evaluation criterion for‘Huashuo'apple harvest maturities were ethylene evolution rate, sugar/acid ratio and starch-iodine index. And the firmness, SSC and starch content could be used as reference indexes. Harvest date Ⅱ was the optimal harvest stage for‘Huashuo'apple fruits. The parameters of sugar/acid ratio, starch-iodine index, ethylene evolution rate of‘Huashuo'apples at this harvest date were(10.57±0.14),(3.40±0.20) and(10.65±0.60) μL · kg-1· h-1,respectively.