Functional properties of pH-shifted protein isolates from bigeye snapper (Priacanthus tayenus) head by-product

Figures & data

Table 1. Salt-solubility and surface hydrophobicity reported as the amount of BPB bound of acid- and alkaline-made protein isolates from bigeye snapper head.

Sample	Salt-solubility (%)	BPB bound (μg)
Acid-made protein isolate	11.0 ± 0.4a*	157.6 ± 1.3b
Alkaline-made protein isolate	16.5 ± 1.4b	118.1 ± 3.9a

All values are given as means ± SD from triplicate determinations.

*Different letters in the same column indicate significant differences (p < 0.05).

Table 2. Textural and color properties of acid- and alkaline-made protein isolate gels from bigeye snapper head prepared with and without NaCl.

Sample	Breaking force (N)	Deformation (mm)	L*	a*	b*	Whiteness	Expressible drip (%)
Acid-made protein isolate without NaCl	ND^#	ND	35.1 ± 0.1b	1.3 ± 0.3a	10.8 ± 0.1c	34.1 ± 0.1b	ND
Acid-made protein isolate with NaCl	0.6 ± 0.1a	1.7 ± 0.3a	35.6 ± 1.1b	1.3 ± 0.4a	11.5 ± 0.3d	34.5 ± 1.0b	40.6 ± 1.7b
Alkaline-made protein isolate without NaCl	ND	ND	28.5 ± 0.3a	3.4 ± 0.0c	9.5 ± 0.2b	27.8 ± 0.3a	ND
Alkaline-made protein isolate with NaCl	1.6 ± 0.4b	3.2 ± 0.5b	27.3 ± 0.1a	3.0 ± 0.8b	8.9 ± 0.1a	26.7 ± 0.1a	33.6 ± 1.7a

All values except for breaking force and deformation are given as means ± SD from triplicate determinations.

For breaking force and deformation, values are given as means ± SD from six determinations.

*Different letters in the same column indicate significant differences (p < 0.05).

^#ND: not detectable because of no gel formed.

Figure 1. SDS-PAGE of bigeye snapper head pH-shifted protein isolates and their gels under (a) non-reducing and (b) reducing conditions. M: Standard molecular weight marker; 1: Original bigeye snapper head; 2: Acid-made protein isolate; 3: Alkaline-made protein isolate; 4: Gel of alkaline-made protein isolate; 5: Gel of acid-made protein isolate. MHC: myosin heavy chains; AC: actin.

Figure 2. Electron microscopic images of protein isolate gels/aggregates prepared by using different conditions (magnification: 10,000 × EHT: 10 kV). (a) Acid-made protein isolate without NaCl; (b) Acid-made protein isolate with NaCl; (c) Alkaline-made protein isolate without NaCl; (d) Alkaline-made protein isolate with NaCl.

Figure 3. (a) Emulsion activity index (EAI), (b) emulsion stability index (ESI), (c) foam ability, and (d) foam stability of acid-and alkaline-made protein isolates and commercial whey protein isolate and egg albumen. Bars represent the standard deviation from triplicate determinations. Different letters indicate significant differences (p < 0.05).