A STUDY ON RHEOLOGICAL PROPERTIES OF TOMATO CONCENTRATES AS AFFECTED BY CONCENTRATION METHODS, PROCESSING CONDITIONS AND PULP CONTENT (VISCOSITY, FLOW PROPERTIES, TOMATO PASTE, FOOD SUSPENSIONS).

摘要

Rheological properties of tomato concentrates made from three concentration methods: juice evaporation (JE), serum evaporation (SE) and serum reverse osmosis (SRO), were studied. SRO concentrates have the highest apparent viscosities while JE concentrates have the lowest apparent viscosities. Apparent viscosities of JE concentrates prepared by concentrating tomato juice to 40% total solids and subsequently diluting to desired concentrations were less than those of the concentrates prepared by straight concentration. Severe heating for a long period of time caused reduction in apparent viscosity.;The values of intrinsic viscosity of serum separated from tomato juice and concentrates subjected to shear and heat were found to follow the same type of response as the viscometric behavior of the juice and concentrates. The magnitude of intrinsic viscosity of serum separated from tomato juice was about the same in magnitude of that of pectin in glucose-citrate buffer solution.;Rheological properties of tomato concentrates containing serum at 5.6, 10.0, 15.0 and 20.0(DEGREES) Brix with varied pulp content between -30% to +30% away from normal weight ratio of pulp:serum were studied. Amount of pulp in tomato concentrates can be adjusted to obtain concentrates having higher or lower apparent viscosity without changing sugar concentration in serum. Linear relationships between added pulp, in terms of % wet weight pulp (WWP), % volumetric pulp (VP) and wet weight ratio of pulp:serum, and apparent viscosities of the concentrates were found. Therefore, more pulp can be added to the concentrated serum to obtain the concentrates which have the same high apparent viscosity as if they were concentrated to higher concentration.;Particle size distribution affected the apparent viscosity of tomato juice and JE concentrates prepared from finisher screen sizes of 0.020, 0.027, 0.033 and 0.045 in. In general, the apparent viscosity increased with increase in finisher screen size. However, JE concentrates and juice from 0.027 in. screen had highest apparent viscosity. Magnitude of yield stress of JE concentrates increased in direct proportion to the finisher screen size.