Biohydrogenation of soybean oil in spray dried casein-oil emulsions from different treatments

The objectives of this investigation were (1) to produce substrates consisting of spray dried casein-soybean oil emulsions treated with different chemical compounds and (2) to investigate the biohydrogenation of the oil in these substrates in vitro using bovine ruminal fluid. Prior to spray drying, substrates, casein: soybean oil, 1:1, w/w, were produced by 7 different treatments: untreated (T1) and treated with acetaldehyde (T2), formaldehyde (T3), peanut skin aqueous extract (T4), tobacco stem aqueous extract (T5), diacetyl (T6) or tannic acid (T7). Two replications were run with a single replication consisting of substrates from the 7 treatments being digested 0 and 23 hr by ruminal fluid. The relative percentages of the following fatty acids: 14.0, 16:0, 16:1, 18:0, 18:1 trans, 18:1 cis, 18:1 isomer, 18:2, 18:3, 20:0, 20:1 and 20:4 were determined in each substrate digest at 0 and 23 hr digestion time. The percentage of each acid was statistically analyzed as a function of treatment, digestion time and their interaction. Micrographs of the spray dried emulsion of each treatment also were obtained by scanning electron microscopy.

When averaged across treatment, the percentages of 18:0 and 18:1 trans increased and the percentage of 18:2 decreased (P<.05) during 23 hr digestion showing that biohydrogenation occurred in the substrates. When averaged across digestion time, the percentages of 18:0, 18:1 trans and 18:1 isomer were higher and the percentages of 18:2 and 20:0 were lower (P<.05) in group 1 treatments (T1, T2, and T5) than in group 2 treatments (T3, T6 and T7). This showed that more 18:2 was biohydrogenated by ruminal microbes to 18:1 isomer, 18:1 trans and 18:0 in group 1 treatments than in group 2 treatments. Group 2 treatments protected the unsaturated fatty acids from biohydrogenation better than group 1 treatments. The fatty acid composition of T4 digests was most like group 1 treatments, and T4 also did not prevent biohydrogenation . During 23 hr digestion, the level of 18:1 trans increased in T1, T2, T4, T5 and T6 but not in T3 and T7. This indicated that T6 was not as effective in preventing biohydrogenation as T3 and T7. The microstructure of emulsions from T1, T2, T4 and T5 were similar to those of spray dried casein in the absence of fat, and the microstructure of emulsions from T3, T6 and T7 were similar to spray dried cheese powders with a protein:fat ratio of approximately 1:1.