Peningkatan sifat prebiotik tepung pisang dengan indeks glikemik rendah melalui fermentasi dan siklus pemanasan bertekanan-pendinginan

Abstract

Banana flour is a potential prebiotic source due to its resistant starch (RS) content. In this study the formation of RS type III (RS3) in banana var agung semeru (Musa paradisiaca formatypica) flour was increased in order to improve the prebiotic properties. RS-rich banana flour can be processed further to produce various kinds of functional foods. The modification process of banana flour production was conducted by a spontaneous submerged fermentation of the banana slices for 24 h at room temperature followed by one or two cycles of autoclaving (121oC, 15 min) and cooling process (4oC, 24 h). The results showed that the modification process influenced the physicochemical characteristics of banana flour. Combination of spontaneous fermentation with two cycles of autoclaving-cooling significantly increased the RS content of the modified flour about four times (28.88%). The spontaneous fermentation produced banana flour with higher amylose content. X-ray diffraction pattern of var agung semeru banana flour could be categorised as C- type granule. The native banana flour showed higher crystalinity (18.74% - 20.08%) than the modified banana flour (6.98% - 9.52%). Phenotypic and genotypic identification showed that Lactobacillus sp associated with the spontaneous fermentation of var agung semeru banana were identified as homofermentative and heterofermentative lactic acid bacteria. They were Lactobacillus salivarius and L. fructivorans. Controlled fermentation using L. salivarius FSnh1 was conducted to produce an equivalent RS content with 24 h spontaneous fermentation. Banana slices were fermented by L. salivarius FSnh1 for 12 and 24 h at room temperature, followed by two cycles of autoclaving-cooling process. The result showed that controlled fermentation using L. salivarius FSnh1 was able to reduce the fermentation time from 24 h by spontaneous fermentation to 12 h and there fore could be recommended to replace the spontaneous fermentation. The modified banana flour showed better prebiotic properties than the native banana flour. The RS3 isolated from modified banana flour was more stable to hydrolysis performed by artificial human gastric juice, able to modulate the growth of lactobacilli and bifidobacteria, produce butyric acid and increase prebiotic index (PI) score (5.14) than RS2 isolated from native banana flour (4.02). The modification process could also produced lower glycemic index (low GI)-banana flour than native banana flour (moderate GI).

Tepung pisang berpotensi untuk dikembangkan sebagai pangan fungsional karena mengandung komponen prebiotik yaitu pati resisten tipe II (RS2). Potensi RS2 untuk dikembangkan sebagai prebiotik memiliki kelemahan karena sifat resisten RS akan hilang jika pati mengalami gelatinisasi selama pengolahan. Oleh karena itu dilakukan modifikasi proses pembuatan tepung pisang kaya pati resisten tipe III (RS3) yang dapat bersifat lebih stabil selama pengolahan melalui fermentasi dan siklus pemanasan bertekanan-pendinginan. Proses modifikasi dilakukan dengan cara fermentasi spontan selama 24 jam pada suhu ruang yang dikombinasi dengan satu atau dua siklus pemanasan bertekanan (121 oC, 15 menit) dan pendinginan (4 oC selama 24 jam). Dua siklus pemanasan bertekanan-pendinginan mampu meningkatkan kadar RS lebih banyak daripada satu siklus retrogradasi. Kadar RS tepung pisang yang tinggi hingga empat kali (dari 7.24% menjadi 28.88% bk) dihasilkan dari modifikasi fermentasi spontan dengan dua siklus pemanasan bertekanan-pendinginan. Granula pati yang pecah akibat proses gelatinisasi selama pemanasan bertekanan kehilangan sifat birefringence dan tingkat kristalinitas tepung pisang menurun dari 18.74 - 20.08% menjadi 6.98 - 9.52%. Hasil difraksi sinar X menunjukkan granula pati pisang var agung semeru adalah granula tipe C yaitu campuran granula tipe A dan tipe B yang memiliki puncak difraksi sinar X pada sudut 17o dan 24o.