The total sugars content (comprising sucrose, glucose, fructose, and xylose) was the highest in the cv. ‘Mohawk’, namely 74.1 g/kg during the time of complete ripeness. The fruits of the cvs. ‘Northeaster’, ‘Evita’ and ‘Fern’ developed high contents of total sugars as well (from 62.8 to 68.6 g/kg), while the fruits of the cvs. ‘Marmolada’, ‘Miss’ and ‘Elsa’ attained very small amounts of total sugars (from 38.8 to 42.7 g/kg).
The content of total acids, comprising the sum of individual acids, decreased with the maturity. This can be due to the negative trend of the citric acid content. The lowest content of total acids was measured in the cv. ‘Miss’, which exhibited also low amounts of sugars. The cv. ‘Elsanta’ had a high content of total acids but a low content of total sugars. Therefore the sugars: acids ratio was low in the cv. ‘Elsanta’ (3.8), and high in the cv. ‘Miss’. In the time of complete ripeness the ratio was the highest in the cv. ‘Mohawk’ due to the high content of sugars.
4. Discussion
Quality is usually estimated from the relative values of several characteristics considered together (Kader, 2000). Quality control starts in the field with the selection of the proper time to harvest for maximum quality. When then is the optimum point in the period of maturity for harvest? Optimum harvest maturity for the grower is a function of both product and marketing conditions. It is not a fixed point in the developmental cycle of a plant, determined by specific physical and/or chemical characteristics of the fruit to be harvested.
Our hypothesis that in the last stage of ripening the fruits not only alter in colour, shape, weight, but also in inner quality proved to be correct. During the time of transition from the stage of technological to the stage of complete ripeness an increase in the contents of sugars and a decrease in the contents of acids mainly determined the alterations. With the exception of the two cultivars ‘Kent’ and ‘Pegasus’, the content of sucrose decreased, and the contents of glucose, fructose, and xylose increased. On average, the total sugars content increased by 6.6 g/kg and in the cvs. ‘Fern’ and ‘Kent’ it increased even by 15.2 and 13.3 g/kg, respectively. The content of total acids was decreased in most of the cultivars due to citric acid reductions. The contents of fumaric and shikimic acids raised; however, an increase was not significant in the content of total acids.
The strawberry cultivars of various genetically and geographical sources which grew in equalised cultivation conditions developed fruits which differed in their chemical compositions. The mean values calculated during the research correspond to those measured by Wrolstad and Shallenberger (1981). The contents of fructose and glucose in the fruits which Wrolstad and Shallenberger chemically analysed reached the values of 22.3 and 23.3 g/kg, respectively. In our research the fruits of the 13 cultivars exhibited the following amounts: 22.3 and 26.2 g/kg of fructose, and 19.1 and 22.3 g/kg of glucose. The mean value of sucrose (6.0 g/kg) measured in the sample fruits in our research was lower than the value measured in the research by Wrolstad in Shallenberger (9.0 g/kg), but the interval was larger in our case, what points to typical characteristics of various strawberry genotypes as they were cultivated in equalised growth conditions. The contents of fructose and glucose are similar also to those measured by Richmond, Brandao, Gray, Markakis, and Stine (1981) in their research, but they reported an even higher value of sucrose (16.4 g/kg). The deviations in the values arrived at in the experiments by various authors can be due to a slight variability of the analysed genotypes or due to a low number of the cultivars analysed during the experiments. In the Slovene research the contents of sucrose in the fruits of the cv. ‘Mohawk’ were 21.7 and 18.5 g/kg, and in the fruits of the cv. ‘Marmolada’ the contents were only 2.8 and 1.1 g/kg. The correlation between sucrose and hexose (glucose and fructose) content in strawberries indicates that the accumulation of glucose and fructose in the fruit is dependent on the hydrolysis of translocated sucrose (Shaw, 1988).
The determination of the malic acid content in the strawberry fruits was not reliable due to the co-elution with fructose. However, Pérez et al. (1997) succeeded in separating the components and thus analysing the content of malic acid that in their research exhibited the value of 1.1 g/kg, and citric acid that reached the value of 3.1 g/kg. The values for citric acid in the fruits in our study extended from 4.4 to 10.5 g/kg. Perkins-Veazie (1995) also report similar contents of citric acid (4.2–12.4 g/kg) which in there research presented 88% of total acids. They detected from 0.9 to 6.8 g/kg of malic acid in the fruits.
The content of TSS is quite stable characteristic of different strawberry cultivars. The results of the organoleptic evaluation of strawberries performed by Wozniak, Radajewska, Reszelska-Sieciechowicz, and Dejwor (1997) displayed that in the fruits with flavour defined as sweet, the sugar:acid ratio was 7:1 and in the fruits defined as acid, this ratio was approximately 6:1. We concluded that the average ratio between total sugars and total acids during last maturation stage had increased from 5.5 to 6.5. Individual values deviated from the mentioned ones and in the time of complete ripeness they were 3.8 in the cv. ‘Elsanta’, and 8.7 in the cv. ‘Mohawk’. This can undoubtedly have effects also on the flavour of fruits.
5. Conclusions
The knowledge of the exact qualitative and quantitative distribution of the sugars and organic acids, characteristic for strawberry fruits, is of capital importance for the evaluation of quality of fruits. The accurate analysis of those components enables us to observe the changes in the production of strawberries and during the storage time. To establish the differences among cultivars it is also necessary to eliminate variability due to growing conditions and the degree of ripeness. We propose that the objective analytical determinations of critical components, in future investigations, should be coupled with subjective evaluations by a taste panel to yield useful and meaningful information about edible quality of fresh fruits.
ปริมาณน้ำตาลทั้งหมด คือ 74.1 กรัม / 'Evita' และ 'เฟิร์น' (62.8-68.6 กรัม / กิโลกรัม) ขณะที่ผลของพันธุ์'Marmolada', 'นางสาว' และ 'เอลซา' บรรลุปริมาณที่น้อยมากของน้ำตาลรวม (38.8-42.7 กรัม /
มีเนื้อหาสูงของกรดทั้งหมด (3.8)
(Kader, /
แต่เปลี่ยนสีรูปร่างน้ำหนัก 'เคนท์' และ 'แรงบันดาลใจ' 6.6 กรัม / กิโลกรัมและ CVS 'เฟิร์น' และ 'เคนท์' เพิ่มขึ้นได้โดย 15.2 และ 13.3 กรัม / shikimic
Wrolstad และ Shallenberger Wrolstad และ Shallenberger วิเคราะห์ทางเคมีมีค่า 22.3 และ 23.3 กรัม / 13 สายพันธุ์แสดงจำนวนเงินดังต่อไปนี้ 22.3 และ 26.2 กรัม / กิโลกรัมของฟรุกโตสและ 19.1 และ 22.3 กรัม / (6.0 กรัม / กิโลกรัม) Wrolstad ใน Shallenberger (9.0 กรัม / กิโลกรัม) Brandao, สีเทา, Markakis และ Stine (1981) ในการวิจัยของพวกเขา (16.4 กรัม / ๆ เป็น 21.7 และ 18.5 กรัม / กิโลกรัมและในผลไม้พันธุ์'Marmolada' เนื้อหาเพียง 2.8 และ 1.1 กรัม / hexose (กลูโคสฟรุกโตสและ) translocated (ชอว์,
ก็ไม่น่าเชื่อถือเนื่องจากการร่วม elution กับฟรุกโตสอย่างไรก็ตามPérez, et al, (1997) 1.1 กรัม / กิโลกรัมและกรดซิตริกที่ถึงค่า 3.1 กรัม / 4.4-10.5 กรัม / กิโลกรัมเพอร์กิน -Veazie (1995) (4.2-12.4 กรัม / กิโลกรัม) ซึ่งในการวิจัยที่นำเสนอมี 88% ของกรดทั้งหมดพวกเขาตรวจพบ 0.9-6.8 กรัม /
TSS Wozniak, Radajewska, Reszelska-Sieciechowicz และ Dejwor (1997) 7: 1 และในผลไม้กำหนดให้เป็นกรดอัตราส่วนนี้อยู่ที่ประมาณ 6: 3.8 พันธุ์'Elsanta' และ 8.7
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