Sains Malaysiana 49(7)(2020): 1577-1583

http://dx.doi.org/10.17576/jsm-2020-4907-10

Physicochemical and Bread-making Properties of Flours from Sweet Potatoes with Different Flesh Colours

(Sifat Fizikokimia dan Pembuatan Roti daripada Tepung Ubi Keledek dengan Warna Isi yang Berbeza)

MOHAMMAD ZAHIRUL ISLAM, JI-YOUNG KIM & YOUNG-TACK LEE*

Department of Food Science and Biotechnology, Gachon University, Seongnam 13120, Republic of Korea

Received: 19 December 2019/Accepted: 23 March 2020

ABSTRACT

Flour was prepared from Korean sweet potatoes (SPs) with different flesh colours (white, yellow/orange, and purple) and evaluated for physicochemical and pasting properties and their partial substitution for bread-making. SP tubers were soaked in sodium metabisulfite solution (anti-browning agent) and subjected to hot air drying, followed by grinding. SP flours with different colours showed variations in chemical compositions, especially amylose, dietary fibre, and starch contents. Yellow/orange-fleshed SP flour had the highest content of total carotenoid (5.26 mg/100 g) among all SP flours. The highest total anthocyanin content (59.92 mg/100 g) was reported for purple-fleshed SP flour. Water absorption index (WAI), water solubility index (WSI), and an oil absorption of purple-fleshed SP flour were 1.63 g/g, 25.59%, and 187.21%, respectively, and relatively higher than those of white or yellow/orange-fleshed SP flour. Wheat flour was substituted with SP flour in bread at 10-30% level. The increase in the proportion of SP flour resulted in a significant decrease in loaf volume, and maximum reduction in loaf volume was reported for the bread containing purple-fleshed SP flour. However, SP flour may serve as a substitute for wheat flour at levels up to 10% without causing any deteriorating effects on the overall bread quality. Therefore, coloured SP flour could be useful in the bread-making industry to improve the nutritional value of bread.

Keywords: Anthocyanin; bread-making; carotenoid; coloured sweet potato; physicochemical properties

ABSTRAK

Tepung disediakan daripada ubi keledek Korea (SP) dengan isi yang berbeza warna (putih, kuning/oren dan ungu) dan dinilai sifat fizikokimia dan adunannya serta penggantian separanya untuk pembuatan roti. Umbi SP direndam dalam larutan natrium metabisulfit (agen anti-pencoklatan) dan mengalami pengeringan udara panas, diikuti dengan pengisaran. Tepung SP dengan warna yang berbeza menunjukkan variasi dalam komposisi kimia, terutama amilosa, serat makanan dan kandungan kanji. Tepung SP berisi warna kuning/oren mempunyai kandungan karotenoid tertinggi (5.26 mg/100 g) antara semua tepung SP. Jumlah kandungan antosianin tertinggi (59.92 mg/100 g) dilaporkan untuk tepung SP berisi warna ungu. Indeks penyerapan air (WAI), indeks kelarutan air (WSI), dan penyerapan minyak tepung SP berisi warna ungu masing-masing adalah 1.63 g/g, 25.59% dan 187.21% dan relatif lebih tinggi daripada tepung SP dengan isi berwarna putih atau kuning/oren. Tepung gandum diganti dengan tepung SP dalam roti pada kadar 10-30%. Peningkatan bahagian tepung SP menghasilkan penurunan isi padu roti yang ketara dan penurunan maksimum jumlah roti dilaporkan untuk roti yang mengandungi tepung SP berisi warna ungu. Walau bagaimanapun, tepung SP dapat berfungsi sebagai pengganti tepung gandum pada kadar hingga 10% tanpa menyebabkan kesan buruk pada kualiti roti secara keseluruhan. Oleh itu, tepung SP berwarna boleh digunakan dalam industri pembuatan roti untuk meningkatkan nilai pemakanan roti.

Kata kunci: Antosianin; karotenoid; pembuatan roti; sifat fizikokimia ubi keledek berwarna

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*Corresponding author; email: ytlee@gachon.ac.kr