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Contents and Losses of Vitamin C in Vegetables During Storage and Cooking

M. R. H. Bhuiya
Bangladesh Agricultural University, Mymensingh.

A. K. M. A. Habib
Bangladesh Agricultural University, Mymensingh.

M. M. Rashid
Bangladesh Agricultural University, Mymensingh.

Abstract/ Executive Summary:

Sixteen vagetables were analysed to follow the losses of vitamin C. during post-harvest storage for 24, 48 and 72 hours at ordinary laboratory temperature (250-300 C). Six other vegetables were also studied to compare the effects of cooking with those of storing vegetables for 72 hours on the rate of loss of vitamin C. All vegetables invariably lost vitamin C during storage. The rate of loss increased with increasing periods of storage. After 72 hours the losses of vitamin C in the case of sponge gourd, bitter gourd, lettuce, bottle gourd greens, ribbed gourd, sweet gourd and sweet gourd greens were more than 50%. Patato, cauliflower, banana and teasle gourd seemed to have retained higher amounts of vitanur. C than did other vegetables over the storage periods. Cooking of vegetables immediately after harvest caused a much greater Joss in vitamin C than that due to post-harvest storage even for 72 hours. Among the vegetables cooked. retention of the vitamin was higher in knolkhol and tomato nnd lower in lady's finger. The average loss of vitamin C due to storage was 29•28%, while due to cooking was 50 43%. The highest loss of the vitamin due to cooking occurred with lady's-finger, which was followed in a decreasing order by cabbage, radish, papaya,tomato and knolkhol.

Keywords: Vitamin C, Vegetable, Cooking

Location: Biochemistry laboratory, Bangladesh Agricultural University, Mymensingh.

Start Date:

End Date:

Program Area: Quality and Nutrition

Commodity: Fodder

Objectives:

To report the degree of loss of vitamin C when the vegetables were stored for 24, 48 and 72 hours or were cooked.

Methodology:

Fresh vegetables were collected from the Bangladesh Agricultural University Horticulture farm and those vegetables which were not available in the farm were collected from local farmers' plots. All analyses for moisture and vitamin C were done in the Biochemistry laboratory, Bangladesh Agricultural University, Mymensingh.For determination of moisture contents, 5g of fresh edible vegetables were sliced and kept in an incubator at 65°C for a period ( usually 48 hours) to reach a constant weight. The loss of weight expressed as percentage of vegetables represents the moisture contents. Another edible portion of the vegetables was analysed for vitamin C. Some more vegetable samples were preserved at laboratory temperature ( 25°C-30°C) for 24, 48 and 72 hours after which both losses in moisture and vitamin C contents were measured. For determination of vitamin C two procedures where followed. In most cases 2,6 dichlorophenol indophenol visual titration method was used (1), and in cases where the colour of the extract interfered with the end-point of titration a second method, indophenol-xylene extraction method, was followed (4).

Visual titration method: Vitamin C stoichiometrically reduces the due 2, 6.dichlorophenol indopbenol to a colourless compound. 50g of the sample and 50 ml of meta phosphoric acid solution were blended in a waring blendor to yield a homogenous slurry. The whole extract was than filtered add washed with metaphosphoric acid solution to make a definite volume (250 ml). Ten millilitre aliquots of the filtrate in triplicate were titrate against the standardised dye.

Indophenol. Xylene extraction method: This procedure is based upon the quantitative decolouration of 2,6-dichlorophenol indophenol by vitamin C. The excess dye was extracted with xylene and measured in a Bausch & Iomb Spectronic 20 spectrophotometer at 500 nm. A hydroquinone blank was used in order to eliminate the values of optical densities due to interfering pigments. The details of the method was given by Robinson and Stotz (4).

Cooking method To determine the effect of cooking, 50 ml of distilled H₂O and a slight amount of common salt were added to 50g of fresh vegetables. The mixture was boiled for 20 minutes in a beaker covered with a watch glass. When the boiling was over, 25 ml of 6 % metaphosphoric acid solution (6g metaphosphoric acid and 16 ml glacial acetic acid diluted to 100 ml) was added and the total mixture was blended in a waring blendor. A quantity of 25 ml of this filtrate was centrifuged and 10 ml of the supernatant liquid was diluted to 100 ml with the metaphosphoric acid solution. Of this final extract 20 ml in triplicate was titrated against the standardised dye and vitamin C Contents were determined.

Source of Information: Bangladesh Horticulture, Vol-5(2), PaG:1-6, Dec:1977

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Six other vegetables were also studied to compare the effects of cooking with those of storing vegetables for 72 hours on the rate of loss of vitamin C. All vegetables invariably lost vitamin C during storage. The rate of loss increased with increasing periods of storage. After 72 hours the losses of vitamin C in the case of sponge gourd, bitter gourd, lettuce, bottle gourd greens, ribbed gourd, sweet gourd and sweet gourd greens were more than 50%. Potato, cauliflower, banana and teasle gourd seemed to have retained higher amounts of vitanur. C than did other vegetables over the storage periods. Cooking of vegetables immediately after harvest caused a much greater Joss in vitamin C than that due to post-harvest storage even for 72 hours. Among the vegetables cooked. retention of the vitamin was higher in knolkhol and tomato nnd lower in lady's finger. The average loss of vitamin C due to storage was 29.28%, while due to cooking was 50 43%. The highest loss of the vitamin due to cooking occurred with lady's-finger, which was followed in a decreasing order by cabbage, radish, papaya,tomato and knolkhol.

Knowledge Management: Journal