Nutritional and Physico-Chemical Evaluation of Grape Varieties

Abstract

This research aimed to analyze the nutritional facts of three types of grape fruits (black, green, and red) and compare their attributes. The study, conducted from May 2018 to December 2018, involved physico-chemical analysis to evaluate various nutritional factors such as water content, carbohydrates, proteins, fat, vitamins, and minerals. Results indicated variations in pH, conductivity, titratable acidity, and Brix% value among the grape samples. Notably, green grapes exhibited the highest acidity, suggesting a dependency on the ripening stage, which correlates with sugar content.

Furthermore, the study highlighted differences in mineral content, with green grapes showing higher levels of potassium, magnesium, calcium, and zinc, suggesting better nutritional value.

Introduction

Grape (Vitis vinifera) is one of the world’s largest cash fruit crops, its coming under family Vitaceae and genus Vitis. Grape is one of the most commonly consumed fruits in the world both as fresh fruit (table grape) and processed fruit such as, wine, grape juice, molasses, and raisins. Department of Agriculture, Sri Lanka, recommended that there are mainly five local grape varieties, namely, Israel Blue, Cardinal, Black Muscat, which are table varieties; Muscat MI, which can be used as both table and wine variety and French MI which is a wine variety.

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The grape belongs to the berry family, which is attached to stem in the form of cluster or bunch of grapes. The grape is one of the most edible foods, having many established nutritional and medicinal properties for consumers. The production of grapes increased in tropical and subtropical countries such as Bolivia, Brazil, Colombia, Peru, Guatemala in South America, Madagascar, Namibia, Tanzania in Africa and Vietnam, China and India in Asian countries.

Quality and type of wine produced from grapes depends on climatic condition of cultivation. Grape cultivation, most often warm climate and cool climate are distinguished. The chemical composition of grapes is different the fruit has a lower content of sugars, and in colder seasons its acidity may be too high.  Egyptians used the grapes for wine, and later the technology was developed in various western countries like Spain, France and Germany etc. Grapes are divided mainly in two groups; with seed and without seed i.e. seedless grapes. The fruits of Israel Blue grapes are dark blue or black in color with a round to oval fruit shape and cylindrical bunch shape.

The grapes are higher in nutritional and medicinal properties. The grape is a good source of water (82%), carbohydrates (12–18%), proteins (0.5–0.6%), and fat (0.3–0.4%), it also contains significant amounts of potassium (0.1–0.2%), vitamin C (0.01–0.02%), and vitamin A (0.001–0.0015%) and also has a small amount of calcium (0.01–0.02%) and phosphorus (0.08–0.01%). Different studies have shown that grapes contain large amounts of antioxidant phytochemicals. Including phenolic, flavonoids, anthocyanin’s, resveratrol and carotenes. The grape is source of unique natural products for the development of valuable medicines and various industrial products. It is well established that the grape is a major source of several phytochemicals. The main biologically active constituent from the grape are known for various medicinal properties in human diseases.

Materials and Methods

There are various types of grapes available in the market. The different types of grapes varieties are cultivated in different part of world. We choose three different types of grape fruits from the local market. We choose red grapes, black grapes and green grapes for our study. We washed all three types of grapes dried and took the weighed amount of grape in a fruit juicer and blend. Then transfer whole and passed through a small size sieve. Then collected and stored these juice samples in the glass bottles in refrigerated for further use. We changed our juice sample every after 3 days and used fresh juice. We used these juice sample in various preparation for analysis of various physico-chemical parameters.

We have tested prepared juice sample for measurement of pH, conductivity, total titratable acidity, viscosity, water content, ash, sodium, potassium, sugar, iron, zinc, magnesium, calcium, protein, fiber and reducing sugar. We used simple techniques of analysis. Most of the routine laboratory instruments, methods and chemicals were used for the analysis.

pH meter and conductivity meter were used for measurement of pH and conductivity of the sample. We have measured two different concentrations of juice i.e. 25 % and 65 % diluted solutions. The titratable acidity of the samples were measured by titration juice (2 g of grape in 100 ml) sample with previously standardized sodium hydroxide solution and phenolphthalein as an indicator. The acidity of the samples was calculated in terms of tartaric acid. Viscosity and density of the grape juice was measured by using viscosity meter and 25 ml picnometer available. The picnometer was cleaned and weighed before filled with juice and water and then weighed again. These weights were used for calculation of density.

Water contents in the grape berry and juice both were calculated. Two berry of all three types grapes were weighed and kept in the previously weighed crucible and then heated in an oven according to AOAC (2000) method [10]. The same way 5 ml sample of grape juice of all types were used. Then the difference in the weights before heating and after heating was calculated. Ash was determined by AOAC (2000) method [10]. Measured quantity of grape sample was crushed in previously heated and weighed crucible. Samples then burn in electric burner and then combustion takes place in furnace at 5500C for 5 hours. Then cooled and weighed as ash of sample.

Protein content was determined by colorimetric method with the help of biuret reagent as a color forming complex. These purple colored complex was measured in a colorimeter at 540nm. Standard protein solution was prepared and both sample and standards were heat at 370C for 10 min to develop a color . Fiber content was measured by giving treatment of dilute sulphuric acid and dilute sodium hydroxide step by step. Measured quantity of grape was crushed and then treated with dilute sulphuric acid (digested) then filtered, washed and treated with dilute sodium hydroxide and again filtered, washed step by step. Then washed with ethanol [12]. Reducing sugar was determined using benedicts reagent.

Mineral Analysis

Different minerals were analyzed by using different instrumental methods. All samples were converted in to ash and ash was digested in HCl and HNO3 acid mixture. Then it was filtered and diluted in 100 ml volumetric flask. This sample solution was used for analysis of different minerals. Sodium and potassium was determined by using flame photometry. Standard solution of sodium and potassium was prepared by using NaCl and KCl salt. Calibration graph was obtained and using calibration curve equation used for calculation of Na & K.

Iron, Calcium, Magnesium and Zinc was determined by using AAS (Atomic Absorption Spectrophotometer) according to [9] AOAC (2000). Standards of Fe, Ca, Mg, and Zn were used from standard provided with the instrument and diluted to the required concentration of each mineral. Absorbance of standard and samples were obtained from the AAS. Then the calibration curve was obtained and equation of straight line obtained used for the final amount of all minerals per 100gm of grape sample.

Result and Discussion

All parameters were tested in triplicate form and the mean of three observations were used for further calculation. The result obtained during analysis of three types of grapes extract was compared with standard value available. The results of all physico-chemical parameters are summarized in table 1. pH obtained of three samples were found in the range of 3.775 (green grape) – 4.14 (red grape). The variable in pH is mostly due to ripeness of the berry of the grape. More ripen berry has more pH value. Conductivity of the samples were found in the range of 1.39 MS/cm (red grape) – 1.553 MS/cm (black grape).

The total titratable acidity was measured in terms of tartaric acid. It was found that 0.712 g/100ml in red grapes and highest 1.065 g/100ml in green grape sample. Also the Brix% value was measured and it was found that 9.5% in green grapes while highest in 15.5%. If we correlate the pH, titratable acidity and % Brix value of three samples it was found that green grape sample was less pH (more acidic), highest acidity value and %Brix (sugar content) is less. While red grapes found higher pH (less acidic), less titratable acidity value and higher % Brix. Mostly acidity in grapes due to tartaric acid and maleic acid present in the grapes. As the berry get ripen the concentration of maleic acid becomes less and acidity is due to tartaric acid.

The methodology involved selecting three grape samples for analysis, including green, red, and black grapes. We evaluated physico-chemical parameters such as pH, conductivity, titratable acidity, and nutrient content using standard laboratory techniques. The mineral content was analyzed using atomic absorption spectrophotometry for sodium, potassium, iron, calcium, magnesium, and zinc.

The results demonstrate significant nutritional variations among the grape varieties, with green grapes showing superior mineral content.

Conclusion

The study revealed that green grapes possess higher nutritional value due to their superior mineral content and lower sugar levels compared to black and red grapes. These findings underscore the importance of considering grape variety for nutritional and medicinal benefits.

References

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