Table 2. FTIR peak range of extracted collagen (ASC and PSC) from sardine fish.

Fish waste materials	Properties	ASC (nm)	PSC (nm)	Peak region assignment
Scales	Amide-A	3,363	3,356	N–H bond (stretching of proteins)
	Amide-B	2,931	2,931	CH2—asymmetric stretch
	Amide-I	1,643	1,643	C = O bond (stretching of proteins)
	Amide-II	1,527	1,530	N–H bond (Bending/C–N stretching of proteins)
	Amide-III	1,219	1,211	C–O bond (stretch/NH bond coupled with C–N stretch)
Skin	Amide-A	3,379	3,387	N–H bond (stretching of proteins)
	Amide-B	2,931	2,924	CH2—asymmetric stretch
	Amide-I	1,643	1,643	C = O bond (stretching of proteins)
	Amide-II	1,535	1,535	N–H bond (Bending/C–N stretching of proteins)
	Amide-III	1,211	1,211	C–O bond (stretch/NH bond coupled with C–N stretch)
Muscles	Amide-A	3,387	3,356	N–H bond (stretching of proteins)
	Amide-B	2,353	2,931	CH2—asymmetric stretch
	Amide-I	1,643	1,643	C = O bond (stretching of proteins)
	Amide-II	1,535	1,527	N–H bond (Bending/C–N stretching of proteins)
	Amide-III	1,211	1,219	C–O bond (stretch/NH bond coupled with C–N stretch)