Physical and chemical indices of apples cv. honeycrisp, treated with ethylene inhibitor depending on cooling mode

Abstract

Honeycrisp is an apple cultivar of American selection with a unique texture and high turgor of flesh, which provides high consumer demand. However, due to the non- simultaneous onset of harvest maturity, the fruits of this variety require multiple harvesting, sensitive to post-harvest cooling, and during storage they are affected by bitter pit, low-temperature burn and flesh browning. Consumers usually prefer to have firm, juicy, tasty and aromatic apples with flesh firmness not less than 4.5 kg / cm². The firmness of the fruits cv. Honeycrisp for sale in the supermarkets should be higher than 6.2 kg/cm². The effect of harvest time, cooling mode and post-harvest treatment with 1-methylcyclopropene (1-MCP) on the change of flesh firmness, total soluble solids content and titratable acidity in apples cv. Honeycrisp during storage was investigated.

The research was conducted in the storage season 2014/2015 at the Department of Fruit Growing and Viticulture of Uman National University of Horticulture. Honeycrisp apples were collected and stored in a branch of the Department - the farm «Yanis», Khotyn district, Chernivtsi region. The apples were harvested from the same trees at harvesting maturity (first collection) and a week later (second collection), taking into account firmness of the flesh, content of dry soluble substances and iodine-starch test. Fruits of homogeneous ripeness degree of the highest commercial grade were selected from typical trees of pomology varieties, accounting units were immediately formed and examined for damage, and placed into paper lined boxes. On the day of collection, the products were cooled to 5 °C overnight, followed by the storage at 2 ±1 ° С and relative humidity 85-90 % (conventional method) or cooled down slowly with a seven-hour exposure at 10 °С and its subsequent decrease by 1 °С per day to storage temperature 2 ±1 °С.

After three days of loading the refrigerator, half of the products were treated with 1-MCP on the recommendation of the manufacturer of the drug «SmartFresh». After 24-hours exposure, the container was removed and the fruits, which were traditionally cooled, were stored in a chamber at temperature of 2 ±1 °C and relative humidity of 85-90 %, and the samples with slow-cooling were maintained in accordance with the procedure described above. Non-treated (control) and experimental products were placed side by side, since ethylene has no effect on 1-MCP processed fruit. Apple organoleptic evaluation was carried out on a ten-point scale after two months of cold storage. The impact of the studied factors was evaluated by the multivariate analysis of variance based on the program «Statistica-6».

It has been found out that, after six months of cold storage, regardless of the picking date, the cooling mode and the post-harvest treatment of 1-MCP, the flesh firmness of apples cv. Honeycrisp within 7.9-8.9 kg satisfies the requirements of the trading network. Post-harvest treatment of the fruit with an ethylene inhibitor does not improve the maintenance of the indicator. After six months of storage, the total soluble solids was found to be higher in the slowly cooled fruits of mass collection, regardless of the 1-MCP treatment. With the same cooling method, the content of soluble solids was 1.1 time higher in late harvested fruits, and post-harvest treatment of 1-MCP somewhat contributes to maintaining their level only in traditionally cooled fruits of late pick.

After six months of storage, the highest content of titratable acidity is ensured by the traditional cooling of the fruits of the mass collection period without 1-MCP treatment. The loss of organic acids was faster in slowly cooled apples of mass collection. Post-harvest treatment of 1-MCP only slightly helps preserve the acidity of slowly cooled apples of both harvesting periods.

The effect of harvesting time and cooling mode on the change in the apple firmness increases with the increasing of storage duration. The indicator mainly depends on the harvesting time and much less on the cooling mode (the effect at the end of storage was 32.3 and 8.6 %, respectively). The change in the content of total soluble solids and titratable acidity depends mainly on the harvesting time (after six months of storage, the effect was 82.1 and 64.5 %, respectively).