Effect of Germination and Fermentation on in vitro Starch and Protein Digestibility of Pearl Millet

A Research Note

NEELAM KHETARPAUL and B.M. CHAUHAN

ABSTRACT Germination of pearl millet grain for 24 hr significantly improved its in vitro starch and protein digestibility. Fermentation of pearl millet sprouts by mixed culture combinations of yeasts and bacteria (Sac- charomyces diastaticus and Lactobacillus brevis; Saccharomyces diastaticus and Lactobacillus fermentum; Saccharomyces cerevisiae and Lactobacillus brevis; and Saccharomyces cerevisiae and Lacto- bacillus fermentum) resulted in a significant increase in protein and starch digestibility. The pearl millet sprouts fermented with mixed culture containing S. diastaticus and L. brevis had the highest in vitro starch digestibility, while the sprouts fermented with the culture con- taining S. cerevisioe and L. fermentum had the highest in vitro protein digestibility. I

INTRODUCTION PRESENCE of antinutrients like phytlc acid and polyphenols in pearl millet (Pew&turn tphoideum) in abundant amounts (Chauhan et al., 1986; Mahajan and Chauhan, 1987) has been known to account for low in vitro digestibility of its proteins and carbohydrates (Mahajan, 1986; Dhankher and Chauhan, 1987a).

Germination and/or fermentation of various food grains and legumes have been effective methods of improving nutritive value as these processing methods reduce the levels of phytic acid and polyphenols (Chompreeda and Fields, 1984; Thomp- son and Serraino, 1985; Kataria et al., 1988). Reduction in phytate during germination (Khetarpaul, 1988; Kumar, 1989) and fermentation (Dhankher and Chauhan, 1987a; Khetarpaul and Chauhan, 1989a) of pearl millet were responsible for im- provement in the HCl-extractable minerals like calcium, phos- phorus, iron, zinc (Khetarpaul and Chauhan, 1989b) and might lead to improvement in the starch and protein digestibility (in vitro) of pearl millet. The objective of our study was to deter- mine the effect of germination as well as that of fermentation of sprouts (by mixed culture combinations of yeasts and bac- teria) on in vitro starch and protein digestibility of pearl millet.

MATERIALS & METHODS

PEARL MILLET GKAINS used for germination and fermentation were procured from the local market in a single lot. For sprouting, the grains were washed and soaked in distilled water for 12 hr at 30°C. The soaked grains were sprouted in petri-plates lined with wet filter paper at 30°C for 24 hr in an incubator.

For fermentation, the fresh sprouts (1OOg) were mixed with distilled water (200 mL), homogenized to a slurry, autoclaved for 20 min at 5 psi, cooled and inoculated with mixed culture combinations of yeasts and bacteria (Saccharomyces diastaticus, Saccharomyces cerevisiae, Lactobacillus brevis and Lactobacillus fermenturn) and incubated at 30°C for 72 hr. Each of the microorganisms had lo5 cells/ml in the mixed culture. Four mixed culture combinations included S. diastu- ticus and L. brevis (SdLb), S. diastaticus and L. fermenturn (SdLf), S. cerevisiae and L. brevis @Lb) and S. cerevisiae and L.fermentum (ScLf). Raw pearl millet flour served as the control. The fermented

The authors are with the Dept. of Foods & Nutrition, Haryana Agricultural Univ., Hisar- 725 004 India.

samples were air-dried in an oven at 65°C for 48 hr and finely ground in a cyclone mill using 0.5 mm sieve.

Pancreatic amylase (porcine pancreas, Sigma Chemical Company, St. Louis, MO) was used to assess in vitro starch digestibility (Singh et al., 1982). The maltose liberated was measured calorimetrically by using dinitrosalicylic acid reagent (Singh et al., 1982). Protein di- gestibility (in vitro) was determined using papsin and pancreatin (Ake- son and Stahman, 1964). Nitrogen content of the soluble supernatant and undigestible residue was determined by the micro-Kjeldahl method (AOAC, 1980).

Protein digestibility (%) = Digestible protein

Total protein x 100

The data were analyzed for analysis of variance (Panse and Suk- hatme, 1961) in a completely randomized design to test for significant differences among the treatments.

RESULTS & DISCUSSION Starch digestibility

The in vitro starch digestibility increased by more than three- fold when pearl millet grains were germinated for 24 hr (Table 1). This increase was further enhanced when the sprouts were fermented by mixed culture combinations of yeasts and bac- teria the highest being in SdLb combination. Improvement in in vitro starch digestibility was similar when the sprouts were fermented by SdLf and SdLb combinations. Possible break- down of starch to oligosaccharides by fermenting microflora (Cronk et al., 1977) may account for improvement in the in vitro starch digestibility during fermentation of sprouts. Sim- ilar improvements in starch digestibility of pearl millet through germination (Kumar, 1989) and natural (Mahajan, 1986) and rubadi fermentation (Dhankher and Chauhan, 1987b) have been reported earlier.

Protein digestibility Germination brought about a pronounced improvement in in

vitro protein digestibility of pearl millet grains (Table 1). On

Table 1 -Effect of germination and mixed culture fermentation on in vitro starch and orotein diaestibilitv of oearl millet

ln vitro digestibility Starch Protein

Treatment (mg maltose/g flour) (%I Control:

Raw pearl millet flour 17.8 f 1.008 51.0 -r- 0.00’ Germinated (24 hr) pearl Millet flour 55.0 f 1.14 77.2 + 0.28 Fermentation:b

SdLb 82.2 2 0.54 79.7 + 0.21 SdLf 65.3 k 1.08 78.6 + 0.19 ScLb 65.7 ‘- 0.82 82.4 + 0.14 ScLf 61.7 c 0.43 90.1 -c 0.19

SE b-d f 0.43 * 0.12 CD (P<O.O5)C 1.48 0.36 a Mean + SD of four replicates. b SdLb, SdLf, ScLb. and ScLf represent mixed culture combinations: SdLb = S. dias-

taticus + L. brevis; SdLf = S. diastaticus + 1. fermenturn; ScLb = S. cerevisiae + L. brevis: ScLf = S. cerevisiae + L. fermenturn.

C Crilical differences determined by ANOVA (P<O.O5). Differences with in/between the fermentation treatments exceeding this value are significant (P-zO.05).

Volume 55, No. 3, 1990-JOURNAL OF FOOD SCIENCE-883

STARCHIPROTEIN DIGESTIBILIN OF PEARL MILLET. . .

further mixed culture fermentation by the combination of yeasts and bacteria, a significant (PcO.05) enhancement in protein digestibility of the pearl millet sprouts was noticed. Germi- nation followed by fermentation of the pearl millet appeared to be more effective than the germination alone, in improving the protein digestibility (in vitro). The changes in protein di- gestibility of the pearl millet sprouts by all mixed culture com- binations were significantly (P < 0.05) different from each other; the sprouts fermented by ScLf combination had the maximum increase in protein digestibility. Production of certain proteo- lytic enzymes (Steinkraus et al., 1965; Odunfa, 1983; Hes- seltine, 1983) by microflora during fermentation may be the reason for improved protein digestibility of pearl millet. An improvement in protein digestibility (in vitro) in germinated and fermented soybean (Boralker and Reddy, 1985) and ru- h&-a pearl millet fermented food (Dhankher and Chauhan, 1987b) were reported earlier.

Overall, germination alone as well as a combination of ger- mination and mixed culture fermentation by the yeasts and bacteria resulted in improved in vitro starch and protein di- gestibility of pearl millet. Fermentation of the pearl millet sprouts was found to be much more effective than germination alone. Germination and fermentation, therefore, offer unique nutri- tional approaches for making starch and protein in pearl millet more digestible.

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MS recieved 11/15/89; accepted 11/16/89.

NMRIMRI OF OIL IN FRENCH-STYLE DRESSINGS. . -From page 764

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CONCLUSIONS

THE MAGNETIC RESONANCE imaging and spectroscopy technique developed is a feasible method for measuring the amount of oil in separable liquid and in emulsified dressings. The procedures are rapid and do not involve chemical extrac- tion to separate the oil/water phases. The procedures are nei- ther invasive nor destructive, thus the analyzed samples remain suitable for consumption.

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The authors thank the NMR Facility at the University of California, Davis, for use of the NT-360 and 2T CSI-2 equipment.

SELECTIVE INHIBITION OF LECTIN. . .From page 868

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884-JOURNAL OF FOOD SCIENCE-Volume 55, No. 3, 1990

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Cell-agglutinating and sugar-specific

MS received 10/27/89; accepted 12/12/89.

Reference to brand or firm name does not constitute endorsement by the U.S. De- partment of Agriculture over others of a similar nature not mentioned.