Enhanced functionality of fermented whey protein using water kefir

Figures & data

Table 1. Changes in the pH, total soluble solids (TSS, °Brix), protein digestibility (%), and sugar profile (g/L) of unfermented (Day 0) and fermented whey proteins (Day 1 to 5).

Parameters	Fermentation Period (Day)						P Value
	0	1	2	3	4	5
pH	6.89 ± 0.01^a	5.30 ± 0.01^b	4.27 ± 0.02^c	3.73 ± 0.01^d	3.51 ± 0.02^e	3.44 ± 0.01^f	<0.05
TSS	1.50 ± 0.00^a	1.40 ± 0.00^b	1.20 ± 0.00^c	1.20 ± 0.00^c	1.20 ± 0.00^c	1.13 ± 0.05^d	<0.05
Protein digestibility	88.48 ± 0.94^b	89.75 ± 0.79^b	92.33 ± 0.87^a	93.69 ± 0.91^a	93.84 ± 1.77^a	94.33 ± 2.05^a	<0.05
Sugars
Fructose	0.41 ± 0.01^c	1.71 ± 0.03^a	0.78 ± 0.01^b	0.37 ± 0.01^d	0.16 ± 0.003^e	0.05 ± 0.001^f	<0.05
Glucose	0.13 ± 0.01^e	1.22 ± 0.06^b	2.68 ± 0.14^a	1.07 ± 0.05^c	0.60 ± 0.05^d	0.16 ± 0.05^e	<0.05
Sucrose	3.36 ± 0.06^a	0.65 ± 0.01^b	0.09 ± 0.002^c	0.04 ± 0.002^c	ND	ND	<0.05

The data presented in the table represent the mean ± standard deviation (n = 3). Values with different superscripts within the same row are statistically significant from each other (P < .05). ND represents not detected.

Table 2. Changes in the solubility (%), surface hydrophobicity (a.u.), and surface charge (mV) of unfermented (Day 0) and fermented whey proteins (Day 1 to 5).

Parameters	Fermentation Period (Day)						P Value
	0	1	2	3	4	5
Solubility	89.44 ± 2.95^c	91.00 ± 2.66^ab	91.17 ± 1.58^ab	92.38 ± 2.65^ab	93.42 ± 1.37^ab	94.11 ± 1.82^a	P < .05
Surface hydrophobicity	387.23 ± 10.1^a	379.90 ± 12.0^a	339.40 ± 5.0^b	325.90 ± 29.2^bc	293.71 ± 29.1^cd	272.72 ± 18.0^d	P < .05
Surface charge	−30.06 ± 0.6^d	−30.33 ± 0.37^d	−31.36 ± 0.92^cd	−32.80 ± 0.40^bc	−33.56 ± 0.92^ab	−34.93 ± 2.10^a	P < .05

The data presented in the table represent the mean ± standard deviation (n = 3). Values with different superscripts within the same row are statistically significant from each other (P < .05). ND represents not detected.

Figure 1. A schematic diagram illustrating the changes to the whey proteins in this study. (a) preparation of water kefir (50 g of kefir grains with 100 g of brown sugar in 1,000 mL) at 25°C and kefir water-based fermented whey proteins (1 g of casein protein, 5 mL of water kefir, and 95 mL of distilled water). (b) Illustration of the linkages between carbohydrates, protein, and non-nutritive compounds. (c) Outcomes of the water kefir fermentation on the whey proteins.

Table 3. Changes in the percentage of secondary protein components (β-sheet, random coil (RC), α-helix, and β-turn) of unfermented (Day 0) and fermented (from Day 1 to 5) whey proteins based on FTIR measurements.

Secondary Protein Components	Peak (1/cm)	Fermentation Period (Day)						P-Value
		0	1	2	3	4	5
β-sheet
	1,614.42	13.28	13.48	13.86	13.04	13.01	13.25
	1,622.13	7.60	7.87	8.27	7.03	6.94	7.20
	1,633.71	12.82	13.14	13.35	12.21	11.99	11.93
β-sheet (Ʃ)		33.70^a	34.49^a	35.48^a	32.28^a	31.94^a	32.38^a	P > .05
RC	1,645.28	12.25^f	12.99^e	13.86^d	15.65^c	16.60^b	17.33^a	P < .05
α-helix	1,654.07	10.58^a	9.19^b	8.91^c	8.89^c	8.64^d	8.52^e	P < .05
β-turn
	1,668.43	10.31	10.19	9.75	9.88	9.70	9.68
	1,681.93	12.58	12.51	12.35	12.81	12.75	11.90
	1,693.50	20.59	20.63	19.65	20.49	20.37	20.19
β-turn (Ʃ)		43.48^a	43.33^a	41.75^a	43.18^a	42.82^a	41.77^a	P > .05
Ratioa		31.39	26.64	25.11	27.54	26.92	26.32

Values with different superscripts within the same row are statistically significant from each other (P < .05).

^aRatio of α-helix to β-sheet.

Table 4. Changes in the total phenolic content (TPC, expressed in mg GAE/100 g) and phenolic compounds (mg/100 g) of unfermented (Day 0) and fermented (from Day 1 to 5) whey proteins.

	Fermentation Period (Day)						P-Value
	0	1	2	3	4	5
TPC	7.50 ± 1.15^a	7.80 ± 0.82^a	8.50 ± 0.57^a	8.50 ± 0.72^a	8.20 ± 1.11^a	7.60 ± 0.98^a	P > .05
Phenolic Compounds
Catechin	0.617 ± 0.012^b	0.619 ± 0.007^b	0.627 ± 0.004^b	0.637 ± 0.004^a	0.634 ± 0.004^a	0.619 ± 0.007^b	P < .05
Chlorogenic	0.088 ± 0.003^d	0.094 ± 0.003^cd	0.095 ± 0.002^bc	0.104 ± 0.005^a	0.101 ± 0.005^ab	0.094 ± 0.003^cd	P < .05
Epicatechin	2.148 ± 0.072^ab	2.122 ± 0.027^b	2.199 ± 0.040^ab	2.299 ± 0.040^a	2.231 ± 0.090^ab	2.161 ± 0.030^ab	P < .05
Quercetin	0.154 ± 0.004^a	0.158 ± 0.004^bc	0.161 ± 0.005^bc	0.167 ± 0.001^a	0.164 ± 0.007^ab	0.158 ± 0.004^bc	P < .05
Rutin	0.207 ± 0.005^a	0.208 ± 0.008^a	0.211 ± 0.008^a	0.216 ± 0.013^a	0.210 ± 0.013^a	0.209 ± 0.002^a	P > .05
Caffeic acid	0.175 ± 0.004^c	0.183 ± 0.004^bc	0.186 ± 0.005^bc	0.192 ± 0.003^a	0.191 ± 0.005^ab	0.183 ± 0.004^bc	P < .05
Ferulic acid	0.135 ± 0.003^c	0.137 ± 0.001^c	0.138 ± 0.002^bc	0.146 ± 0.002^a	0.143 ± 0.003^ab	0.137 ± 0.002^c	P < .05
Gallic acid	0.066 ± 0.004^b	0.071 ± 0.003^b	0.073 ± 0.005^b	0.084 ± 0.004^a	0.082 ± 0.003^a	0.071 ± 0.003^b	P < .05
Sinapic acid	0.467 ± 0.014^b	0.476 ± 0.010^ab	0.486 ± 0.010^ab	0.494 ± 0.010^a	0.491 ± 0.009^a	0.476 ± 0.010^ab	P < .05
Syringic acid	0.249 ± 0.005^c	0.259 ± 0.003^b	0.263 ± 0.006^b	0.287 ± 0.006^a	0.287 ± 0.001^a	0.259 ± 0.003^b	P < .05
Phenolic Compounds (Ʃ)	4.31	4.32	4.44	4.62	4.54	4.36

The data presented in the table represent the mean ± standard deviation (n = 3). Values with different superscripts within the same row are statistically significant from each other (P < .05).

Figure 2. Microbial activity of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeasts in the fermenting medium throughout the water kefir fermentation of whey proteins.