Development of Vacuum-Steam Combination Heating System for Pasteurization of Sprout Barley Powder

Abstract

The processing of sprout vegetables in powder form has been known to extend the shelf-life by retaining nutritional values; however, sprout powder products were exposed to a variety of contaminants, such as microbial contaminants, during processing and storage. Therefore, the proper treatment for removing the contaminants in the powder was required without compromising their quality properties. This study was conducted (1) to determine a suitable pasteurization method for sprout barley powder, and (2) to investigate the effect of vacuum-steam heating combination treatment on the quality change and the lethality of microorganisms in sprout barley powder. The heating pattern of sprout barley powder was elucidated with a vacuum-thermal combination system consisting of a vacuum chamber, overhead stirrer, far-infrared heater, and PID (Proportional-Integral-Differential) controller. In addition, the mixing patterns of sprout barley powder, depending on the types of stirring blades, were evaluated by discrete element modeling using EDEM™ software. The vacuum-steam combination heating system was fabricated using the investigated pre-design factors. The quality change in sprout barely powder was evaluated by measuring the microbial inactivation, CIE values (L*, a*, b*, ΔE), and water activity (aw). During the pasteurization process, steam could be directly injected into the chamber at regular intervals for two hours to transfer moisture and heat to the powder. By combining steam and vacuum conditions, the population of E. coli O157:H7 in the powder was reduced by 4.33 log CFU/g, eliminating all E. coli O157:H7 in the powder. In addition, the water activity (aw) of the powder was significantly decreased in a vacuum pressure environment without the quality deterioration.

Modification of a Grain Moisture Conditioner into a Vacuum Steam Pasteurizer

“…The purpose of the apparatus is to mimic the pasteurization process conditions of the VSP system from previous lab-scale experiments conducted on LMFs like wheat, flaxseed, and peppercorn [6][7][8][9][10] in a larger sample volume. These conditions include preheating the product to >40 • C, lowering the chamber pressure to 32.4 kPa absolute pressure, injecting steam to reach a temperature of 65 • C to 85 • C for 1 to 8 min, and, finally, removing steam through a vacuum.…”

“…On average, these setups yielded a reduction of 5.09 log CFU/g for Salmonella and 7.34 log CFU/g for E. coli without significantly affecting the color and moisture content. A study by Huang et al [9] yielded a 4.33 log reduction of E. coli 0157:H7 in sprout barley powder after 2 h of VSP on a larger sample of 5 kg with the addition of an agitator for mixing. The moisture content of the powder was significantly reduced due to the addition of vacuum, and direct steam caused a significant discoloration.…”