Improvement of Pacific White Shrimp (Litopenaeus vannamei) Drying Characteristics and Quality Attributes by a Combination of Salting Pretreatment and Microwave

Abstract

This study investigated the effects of salting pretreatment and microwave (MW) power on drying characteristics, water distribution and quality attributes of Pacific white shrimp (Litopenaeus vannamei). With increasing salt concentration (0-8%, w/v) and MW power (300-900 W), the drying time of shrimp was shortened by 15.15-28.57%, compared with the untreated samples. Regarding the quality of dried shrimp, increasing the salt concentration and MW power increased the hardness (from 13,073.6 to 24,556.5 g), while the springiness, color parameters and astaxanthin content showed an initial decrease but a later increase trend. Low field nuclear magnetic resonance (LF-NMR) demonstrated that the T₂ curve of the pretreated samples moved toward the negative x-axis and the immobilized water content decreased with increasing salt concentration. E-nose showed that volatile components were different and could be obviously distinguished at different salt concentrations and MW powers. Raman spectroscopy illustrated that the protein secondary structure of dried shrimp was altered by salting pretreatment and drying conditions, and the lowest conversion degree of α-helix to β-sheet of dried shrimp was obtained at the salt concentration of 4% (w/v) and MW power of 500 W. By comprehensively considering the drying time and quality attributes, the combination of 4% (w/v) salt and 500 W MW power was concluded as the best drying conditions for shrimp using a microwave. The results could provide an innovative combination of salt pretreatment and MW drying with suitable processing conditions for producing high-quality dried shrimp.

Keywords: astaxanthin; microwave drying; protein secondary structure; salting pretreatment; water distribution.

Figure 1

Effect of different salt concentrations and microwave power on drying rate of white shrimp.

Figure 1

Effect of different salt concentrations and microwave power on drying rate of white shrimp.

Figure 2

T₂ relaxation time distribution curves of dried shrimps by different drying treatments: fresh shrimps with different salt concentrations (a), dried shrimps with different salt concentrations (b), dried shrimps with different MW powers (c).

Figure 3

Effects of salt concentration and MW power on color parameters of dried shrimps by MW drying. (A) L*; (B) a*; (C) b*; (D) ΔE. Different letter indicates statistically significant difference at p < 0.05 according to the Duncan test.

Figure 4

Correlation matrixes between the determination parameters. DT: drying time; AST: astaxanthin.

Figure 5

PCA diagram of volatile components in dried samples with different salt concentrations (A) and MW powers (B).

Figure 6

Raman spectra (A) and different proportions of secondary structures of proteins under different heating treatments of dried shrimps (B) (a.u.: arbitrary units). Different letter indicates statistically significant difference at p < 0.05 according to the Duncan test.

Figure 6

Raman spectra (A) and different proportions of secondary structures of proteins under different heating treatments of dried shrimps (B) (a.u.: arbitrary units). Different letter indicates statistically significant difference at p < 0.05 according to the Duncan test.

Figure 7

Changes in total astaxanthin content (μg/g) (dry weight) of shrimps after MW drying under different salt concentrations and MW powers. Different letter indicates statistically significant difference at p < 0.05 according to the Duncan test.

Figure 8

Effect of different salt concentrations on the microstructure of dried shrimps (500×) at a fixed MW of 500 W (A); the effect of different microwave powers on the microstructure of dried shrimp (500×) at a fixed salt concentration of 4% (B).