Effects of microfiltration conditions on filtration performance and cold sterilization of Thai rice wine model

Abstract

This research studied effects of 1) solid-liquid separations of fermented liquor by filtration through cheesecloth, sedimentation for 3 hrs., and centrifugation at 3000xg for 30 min. ; 2) operating conditions of microfiltration such as membrane pore size (0.10, 0.22, and 0.45 u m), transmembrane pressure (∆P at 138, 276, 414, and 552 kPa), and stirring speed (0 and 100 rpm); and 3) size, distribution and concentration of suspended solids on microfiltration performance in terms of permeate flux and specific cake resistance (α), as well as microfiltered rice wine characteristics including pH, titratable acidity, alcohol content, total soluble solids content, total suspended solids content, and yeast, bacteria, and lactic acid bacteria counts. Microfiltration was used to eliminate microorganisms and suspended solids in rice wine for cold sterilization. The results showed that the three solid-liquid separation methods affected concentration, size, and size distribution of suspended solids as well as yeast and bacteria counts. Centrifugation gave the lowest suspended solid concentration (0.02 wt%) as well as size and size distribution (0.3-20 um) and resulted in the greatest permeate flux and α. However, the separation methods did not affect the characteristics and taste of microfiltered rice wine. Microfiltration could eliminate microorganisms since the microorganisms were not detectable in the microfiltered rice wine. Thus, microfiltration could be used for cold sterilization of rice wine. In addition, the results showed that the correlation of the α and the suspended solid concentration (C; wt%) for all size and size distributions (1-20, 1-200, and 1-400 um) could be expressed as α = j + kC where j and are the empirical constants. At the same concentration, the greater the size and size distribution of suspended solids, the lower the α. Moreover, for all suspended solid concentration (0.2, 0.5, and 1.0 wt%), as wt% of suspended solids which having size ≥ 45 um (W) increased, the α decreased. The correlation could be expressed as α = x(l/eyw) with a high correlation (r2 > 0.99), where x and y are the empirical constants.