Rheological and physicochemical properties of vegetable juices and concentrates: A review

Abstract

This review, summarizes the physicochemical and rheological properties (RP) of beetroot (Beta vulgaris L.), carrot (Daucus carota L.), celery (Apium graveolens L.), coriander (Coriandrum sativum L.), fenugreek (Trigonella foenum-graecum L.), kale (Brassica oleracea L.), spinach (Spinacia oleracea L.), and tomato (Solanum lycopersicum L.) juices, and their concentrates. Carbohydrates, crude fiber, organic acids (ascorbic, citric, malic, and oxalic acids), vitamins (A, B, C, and E), minerals (calcium, potassium, and magnesium), amino acids, and phenolic compounds (PC) are major constituents of vegetable juice (VJ). If consumed in sufficient amount, VJs contribute to nutritional requirements for good health in humans. Vegetable concentrates are typically non-Newtonian fluids in which the apparent viscosity decreases with increasing shear rate. The apparent viscosity of VJs decreases at higher temperatures. Several equations are employed to describe flow behavior, but most are difficult to use and none give good overall agreement with experimental data from Power-law and Herschel–Bulkley models. The effect of temperature on apparent viscosity of VJ is generally expressed by the Arrhenius relationship and the activation energy (Ea) for the fluid flow increases with concentration. The Ea values reported for the vegetable products were between 3.6 and 39.7 kJ∙mol−1∙K−1. Higher Ea indicates apparent viscosity is more prone to temperature change. Practical applications Juice can be extracted from fresh vegetables to be used without further change or as concentrates in value added products. Rheological study of vegetable juice, in part how it flows, is important to handling and processing, quality control, and sensory evaluation of derived products. In this study, properties of vegetable juices and concentrates were reviewed. Vegetable concentrates are typically non-Newtonian fluids. The Power-law and Herschel–Bulkley models were successfully applied to fit data. Arrhenius model parameters for some VJs at different concentrations were reported in this study. Higher activation energy indicates viscosity is more prone to temperature change. The activation energy values for the vegetable products were between 3.6 and 39.7 kJ/mol∙K.