Study of sorption isotherms of grape pulp (Siah-e-Sardasht cultivar)

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AGHAZADEH N.; ESMAIILI M.; MOHTARAMI F.

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Journal: ELECTRONIC JOURNAL OF FOOD PROCESSING AND PRESERVATION Year:2019 | Volume:10 | Issue:2 Page(s): 33-44

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Title

Study of sorption isotherms of grape pulp (Siah-e-Sardasht cultivar)

Author(s)

AGHAZADEH N. | ESMAIILI M. | MOHTARAMI F. | Issue Writer Certificate

Keywords

Equilibrium humidity;Grape pulp (SiahQ1

eQ1

Sardasht Cultivar);Isosteric heat of sorptionQ1

Sorption isothermQ2

Abstract

Background and objectives: Organic black grapes produced in Sardasht, West Azerbaijan province in Iran, contain resveratrol and flavonoids and high amount of melatonin with health benefits. The relationship between equilibrium moisture content and water activity at specified temperature is expressed as sorption isotherms. Moisture sorption isotherms are useful in predicting shelf-life stability and in calculating the variations of moisture content during drying, storage and packaging. In physical, chemical and microbial analysis of food, data obtained from adsorption and desorption curves are very important factors. Isotherm curves are able to predict the maximum moisture retention in foods during processing. In this study, the moisture sorption isotherms of grape pulp (Siah-Sardasht cultivar) were determined using a static-gravimetric method at 30, 40, 50, 60 and 70° C with water activities over the range of 0. 1-0. 9. Material and methods: Black grapes were obtained from a vineyard in Sardasht (West Azerbaijan province). Nine saturated salt solutions with degree of purity over 98% were used for generating a range of relative humidity. In order to describe the sorption moisture isotherms, the BET, GAB, Henderson, Darcy-watt and Halsey equations were tested to fit the experimental data by using non-linear regression analysis method. The models were sorted based on the least mean absolute percentage error (P<10%), RMSE and χ 2, and the highest R-square. The isosteric heat was determined using the Claussius– Clapeyron equation. Results: At all of temperature levels, moisture sorption isotherm curves of grape pulp were of type III, according to BET. Moisture sorption isotherms obtained in this work were affected by temperature, and the equilibrium moisture content generally increased with temperature elevation. According to the evaluated parameters in the tested models, P-value of Darcy-Watt model was consistently less than 10 % and its RMSE and χ 2 were lowest, indicating its reliability in predicting moisture sorption behavior of grape pulp. According to results of predicting moisture sorption in the grape pulp, it is concluded that BET and GAB models can be used only at high temperatures. The isosteric heat showed a marked increase with decreasing moisture content especially at the levels less than 0. 3% (d. b). Conclusion: At the studied range of water activity, the equilibrium moisture content values of grape pulp increased with increasing temperature, and no reverse temperature effect was observed in the range of water activities studied here. In spite of presence of sugar in the black grape pulp, no inversion phenomenon was observed in the relationship between equilibrium moisture content and water activity. Darcy-Watt was found to be the best model offering fits over the entire water activity and temperature range. The isosteric heat decreased with increasing the moisture content probably due to the fact that pulp water properties approached to that of free water.

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APA: Copy

AGHAZADEH, N., ESMAIILI, M., & MOHTARAMI, F.. (2019). Study of sorption isotherms of grape pulp (Siah-e-Sardasht cultivar). ELECTRONIC JOURNAL OF FOOD PROCESSING AND PRESERVATION, 10(2 ), 33-44. SID. https://sid.ir/paper/383998/en

Vancouver: Copy

AGHAZADEH N., ESMAIILI M., MOHTARAMI F.. Study of sorption isotherms of grape pulp (Siah-e-Sardasht cultivar). ELECTRONIC JOURNAL OF FOOD PROCESSING AND PRESERVATION[Internet]. 2019;10(2 ):33-44. Available from: https://sid.ir/paper/383998/en

IEEE: Copy

N. AGHAZADEH, M. ESMAIILI, and F. MOHTARAMI, “Study of sorption isotherms of grape pulp (Siah-e-Sardasht cultivar),” ELECTRONIC JOURNAL OF FOOD PROCESSING AND PRESERVATION, vol. 10, no. 2 , pp. 33–44, 2019, [Online]. Available: https://sid.ir/paper/383998/en

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