Influence of micronization on physicochemical properties of dried moso-bamboo shoots

Abstract: Bamboo shoots are widely used in food processing. Many ageing bamboo shoots, which are rich in dietary fiber and protein, contain crude fiber and are of bad taste. In recent years, the micronization technology has been applied in food industries. The aim of this study was to investigate the effect of micronization on the physicochemical properties of dried bamboo shoots. In this study, the coarse powder was processed by vibrational micronization (with cooling system) after coarse grinding. The new technology, which is more efficient than ball grinding, was applied to obtain micronized power. By strong- and high- frequency vibration from an eccentric motor, the samples in the grinding chamber were fluidized under the combined effects of high intensity hit, cut and grind from grinder's rod and wall. Huge mechanical force was produced between grinding media and materials, while the cooling system controlled the grinding temperature. The micronized powders were obtained, their particle sizes, powder flowability, water holding capacity, and swelling were studied. The results indicated that the particle sizes of coarse powders become 18.67 μm and 10.35 μm after micronizing for 30 min and 60 min, respectively. The lightness index (L*) changed from 79 to 90, the yellow depth index (b*) was reduced from 23 to 11, and the red depth index (a*) reduced from 4 to 1. Thereby the colour of the micronized powder looked more uniform and brighter, which improves the appearance quality of bamboo shoots powder. The angles of repose of two kinds of ultrafine powders increased from 36.3° to 49.8° and 51.2°, respectively. The sliding angle increased from 50.8° to more than 69.6°. Both were significantly higher than those of coarse powders (P<0.05). The bulk density reduced from 0.37 to 0.26 g/mL, but no significant change was found for the rap density. This made the compressibility nearly doubled, which changed from 22.8 to 46.9 and 48.5, It is showed that the flow properties of powders were poor after micronization. Compared to coarse powder, water holding capacity of micronized powders was reduced from 5.75 to 3.71 g/g after micronized for 30 min, it further decreased to 3.35 g/g after 60 min micronization. The effect of micronization on oil holding capacity was smaller than water holding capacity. The oil holding capacity reduced significantly (P<0.05) from 2.2 to 1.75 g/g only after 60 min micronization. Micronization decreased the final swelling degree from 8.65 to 6.57 and 7.20 mL/g, but the swelling speed was significantly improved. The micronized powder (particle size of 10.35 μm) can reach to 3.63 mL/g in 15 min, while the shoot's coarse powder (particle size of 298 μm) was only 0.97 mL/g. The above properties suggest that the vibrational micronization is an effective technology. The micronized powder with many characteristic changes can be applied usefully in food industries.