Rice protein hydrolysates as natural emulsifiers for an effective microencapsulation of orange essential oil by spray drying

Figures & data

Figure 1. Interfacial tension at the interface between orange oil and rice protein isolate (RPI) and rice protein hydrolysates (RPH, with the degree of hydrolysis of 2, 6, and 10%) at 1.5% w/w.

Figure 2. Comparison between droplet size and interfacial tension of emulsions of orange oil stabilized by maltodextrin and rice protein isolate (RPI) or rice protein hydrolysates (RPH, with degree of hydrolysis of 2, 6, and 10%).

Figure 3. The size distribution of oil droplets in emulsions stabilized by maltodextrin and either rice protein isolate (RPI) or rice protein hydrolysate (RPH) with degrees of hydrolysis of 2%, 6%, and 10%.

Table 1. Effect of degree of hydrolysis (2, 6, and 10%) on the surface composition obtained from XPS for the spray-dried orange oil powders.

Sample	Level 1^a			Level 2			Level 3			% Protein^b
	C (%)	O (%)	N (%)	C (%)	O (%)	N (%)	C (%)	O (%)	N (%)
RPI	75.71	21.42	0.19	80.16	16.70	0.17	81.79	14.94	0.13	1.07
RPH2	84.25	11.87	0.16	84.62	11.62	0.16	85.52	10.69	0.18	0.56
RPH6	76.59	20.04	0.40	81.05	15.70	0.35	83.13	13.79	0.14	2.24
RPH10	75.63	21.71	0.41	80.49	16.82	0.19	82.44	14.86	0.08	2.30

RPI is rice protein isolate, and RPH is rice protein hydrolysate.

^a XPS measurement depth. Level 1 corresponds to the particle surface; level 2 is an approximate 0.2 nm depth; and level 3 is a 0.3 nm depth.

^b Calculated using N × 5.61^[41] referring to level 1.

Table 2. Physicochemical properties of orange oil microparticles formulated with maltodextrin (MD) and rice protein isolate (RPI) or rice protein hydrolysate (RPH, with degrees of hydrolysis of 2%, 6%, and 10%).

Sample	Hygroscopicity (g H2O/100 g)	Moisture (% wet basis)	Water activity (aw)	D4,3 (μm)	Span	Powder recovery (%)	Oil retention (%)
RPI	8.97 ± 0.10^b	0.87 ± 0.26^a	0.116 ± 0.00^a	19.75 ± 2.04^a	2.11 ± 0.21^a	21.47 ± 1.47^b	23.03 ± 3.35^b
RPH2	9.93 ± 0.20^a	1.16 ± 0.71^a	0.129 ± 0.00^a	13.35 ± 1.04^b	2.02 ± 0.11^a	24.08 ± 1.52^b	24.77 ± 0.31^b
RPH6	10.09 ± 0.19^a	0.57 ± 0.12^a	0.075 ± 0.00^a	14.68 ± 0.81^b	1.97 ± 0.10^a	27.19 ± 0.19^a	47.95 ± 3.35^a
RPH10	9.65 ± 0.35^a	0.75 ± 0.20^a	0.114 ± 0.02^a	13.28 ± 0.58^b	1.91 ± 0.12^a	25.89 ± 0.11^a	49.97 ± 0.75^a

Different letters represent statistically significant differences (P < 0.05).

Figure 4. Particle size distributions for microparticles produced by rice protein isolate (RPI) or rice protein hydrolysate (RPH, with degree of hydrolysis of 2%, 6%, and 10%).

Sosulski, F. W.; Imafidon, G. I. Amino Acid Composition and Nitrogen-to-Protein Conversion Factors for Animal and Plant Foods. J. Agric. Food Chem. 1990, 38, 1351–1356. DOI: 10.1021/jf00096a011.

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