Sea Bass Fish Head Broth Treated by Thermo-Ultrasonication: Improving the Nutritional Properties and Emulsion Stability

Abstract

This work investigated the underlying mechanism of thermo-ultrasonic treatment to improve the nutritional properties and emulsion stability of sea bass fish head broth. The effects of ultrasonication on the processing of fish broth were compared with boiling water treatment. The nutritional properties of fish broth mainly include protein, fat, total sugar, 5'-nucleotide and free amino acid content. To achieve a similar effect of nutrient extraction, the thermo-ultrasonic treatment required a shorter time (30 min) than boiling water (120 min). The water-soluble protein, fat and total sugar contents were at their maximum at 120 min of the thermo-ultrasonic treatment. In particular, the fat content increased with the time of thermo-ultrasonic treatment from 0.58% to 2.70%. The emulsion structure of the fish soup was characterized by measuring its color and particle size, using optical microscopy and confocal laser scanning microscopy, and determining its storage stability. Thermo-ultrasonic treatment reduced the particle size of the fish broth emulsion and the fat globules became smaller and more homogeneous. Ultrasonication not only accelerated the nutritional and flavor content of the fish head broth, but also reduced the particle size and enhanced the stability of the emulsified system of the fish broth. The fish head tissue was more severely disrupted by the cavitation effect of an ultrasound, and nutrients migrated more and faster. This was mainly due to the cavitation and mechanical breaking force of the ultrasound on the fish head tissue and the fat globules of the fish broth. Altogether, these findings suggest that the thermo-ultrasonic treatment technique is useful for processing nutrient-rich, storage-stable and ready-to-eat fish head broth.

Keywords: emulsion stability; nutritional properties; sea bass fish head broth; thermo-ultrasonic treatment.

Figure 1

Changes in protein (A), fat content (B) and total sugar (C) by boiling water and thermo-ultrasonic treatment with different treatment times (0, 30, 60, 90, 120 min). The contents and TAV of 5′-GMP (D), 5′-AMP (E) and 5′-IMP (F) by boiling water and thermo-ultrasonic treatment with different treatment times (0, 30, 60, 90, 120 min).

Figure 2

Heat map of the free amino acid content of fish broth (A) and the breakdown of the different types of free amino acids (B) by boiling water and thermo-ultrasonic treatment with different treatment times (0, 30, 60, 90, 120 min).

Figure 3

L* (A) and d_3,2 (B) values of fish broth by different treatments and times. Droplet size distribution of fish broth by boiling water (C) and thermo-ultrasonic treatment (D) with different treatment times (1–5—0, 30, 60, 90, 120 min). The capital superscript letters (A and B) represent significant differences between treatment groups A and B, while small superscript letters (a, b, c, d, e) represent significant differences among treatment times (p < 0.05).

Figure 4

Optical micrographs of fish broth prepared by boiling water (A) and thermo-ultrasonic treatment (B) with different treatment times (1–5—0, 30, 60, 90, 120 min; Bar = 50 μm).

Figure 5

Confocal laser scanning micrographs of fish broth prepared by boiling water (A) and thermo-ultrasonic treatment (B) with different treatment times (1–5—0, 30, 60, 90, 120 min; Bar = 10 μm).

Figure 6

Appearance of the fish broth after storage at 1, 3, 5, 7 days by boiling water (A) and thermo-ultrasonic treatment (B) with different treatment times (1–5—0, 30, 60, 90, 120 min).

Figure 7

The correlation analysis of substances and droplet sizes of fish broth prepared by boiling water (A) and thermo−ultrasonic treatment (B) with different treatment times (0, 30, 60, 90, 120 min).

Figure 8

Schematic diagram of the thermo-ultrasonic treatment on fish broth.