Influence of storage duration on the biochemical composition of potato tubers of different maturity groups

Abstract

During storage in the biochemical composition of potato tubers, significant changes can occur that depend on varietal characteristics, the group of maturity, duration and storage regimes. Therefore, the purpose of our research was to determine the effect of long-term storage on changes in the biochemical composition of potato tuber varieties which belong to different groups of maturity.

In the studies were used 5 varieties of potatoes from HZPC (Netherlands) and Solana (Germany) which belong two groups of maturity: medium-early (Satina – control, Red Lady, Mozart) and medium-ripe (Arosa – control, Sifra). The tubers were grown under the conditions of Biotech LTD. Determination of biochemical quality indicators of tubers was carried out in the laboratory of the Department of storage, processing and standardization of plant products after prof. B.V. Lesik of the National University of Life and Environmental Sciences of Ukraine in 2013-2015. In potato tubers, before storage and after 2, 4 and 6 months were determined dry substances, starch and sugars (total and reduced). For conducting biochemical analyzes used 10 kg of potato tubers of each variety which storage.

         As a result of the conducted research, it was found that during storage of potatoes of experimental varieties in potatoes there is a decrease in the amount of dry matter, but the intensity of their change was not the same.

         The group of ripeness has had a significant impact on the accumulation of dry matter. Thus, on average in the medium-early group, at the beginning of storage, the dry matter content was 23.5%, while in the medium-ripe group 29.3%. At the end of storage, the average values for groups were: 21.1% and 25.9%, respectively. Absolute losses, on average in both groups, comprised for the whole period from 2.4 to 3.4%, and relative, from 9.8 to 11.7%. The difference in losses between individual varieties was more significant and ranged from 2.1% for the Mozart variety to 3.6 for the Arose variety. Especially intensively was lost solids in the third period of storage from 4 to 6 months, which can be explained by the intensification of physiological processes in potato tubers in the spring. The influence of the ripeness group on the amount of losses was not established. They were influenced by the initial amount of dry matter: in larger quantities before the storage – they were more lost during the period of storage.

         The basis of dry matter in potato tubers is starch, the content of which correlates with them, and the difference is about 5-9 absolute percent.

         In our studies, the average starch of potato tubers, depending on the group of maturity, increased from 16.5% in the medium-early to 23.7% in the medium-ripe. This indicator was more dependent on varietal characteristics.

The obtained results testify that on the index of starch, the medium-ripe varieties varied: from 21.8% in Sifra to 25.5% in Arosa. In the medium-early group, this difference was less - from 15.5% in Mozart to 17.7% in Red Lady.

         Storage for 6 months did not cause significant changes in the starch content of tubers. Thus, on average, over three years of research, absolute losses were: in the medium-early group - 1%, in the medium-ripe group - 1.9%, and relative - 5.9% and 8.2%, respectively. High levels of starch after 6 months of storage were characterized by Arosa (23.3%) and Sifra (20.1%) varieties, which allows them to recommend these cultivars for starch and alcohol cultivation throughout the entire processing season.

The content of sugars in tubers can very greatly depending on varietal characteristics, the state of tubers and storage conditions. In young potatoes, sugar is larger than in ripe. Bulbs, which have a higher content of sucrose than monosaccharides, have better storage capacity. The ability to accumulate monosaccharides as a result of the hydrolysis of starch at low storage temperatures of tubers is particularly important in terms of varietal characteristics.

In our studies, the total content of sugars in the three years of research was on average in the medium-early group - 0.43%, and in the medium-ripe group - 0.4%.

         On average, over the years of research, the total content of sugars practically did not differ between groups of maturity, however, there were differences between individual varieties. The largest content of sugars contained variety of Satina (0.65%), and the smallest varieties Sifra (0.22%) and Mozart (0.23%). The content of the reduced sugars in the tubers varied from 0.07% to 0.28%, making them suitable for industrial processing.

The process of storage was accompanied by an increase in the content of both general and reduced sugars. For the start period of storage, the total content of sugars has increased from 2 to 5 times depending on the variety, and reduced to at least five times and at the end of storage (after 6 months) ranged from 0.4% to 0.65%.

That is, for most varieties, the typical excess of optimal content was 0.2-0.4%, which makes them unsuitable for the production of fried potato products.

         Thus, it was established that the process of storing potato tubers is accompanied by loss of dry matter, especially in the period from 4 to 6 months, which can be explained by the intensification of physiological processes in potatoes in the spring. The influence of the maturity group on the amount of losses was not established. All potato varieties had a high content of starch, and storage did not have a significant impact on the amount of its losses (in the medium-early group - 1%, in the medium-ripe group - 1.9%). The highest content of starch after 6 months of storage was characterized by varieties Arosa (23.3%) and Sifra (20.1%), which allows recommending these varieties for cultivation in order to obtain starch and alcohol.

         The amount of total sugars depends on the varietal characteristics of the potato and does not depend on the group of maturity: the highest content was characterized by the Satina variety (0.65%), and the smallest - Sifra (0.22%) and Mozart (0.23%). For the whole period of storage, the total content of sugars has increased from 2 to 5 times, depending on the variety. The amount of sugar reduced during storage increased by at least five times and in the 6 months it ranged from 0.4% to 0.65%.