Malays. Appl. Biol. (2011) 40(1): 19-23
PECTINS FROM DRAGON FRUIT (Hylocereus polyrhizus) PEEL
NAZARUDDIN, R.1*, NORAZELINA, S.M.I.1, NORZIAH, M.H.2 and ZAINUDIN, M.3
1School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia
2School of Industry Technology, Universiti Sains Malaysia, 11800 Minden, Pulau Pinang, Malaysia
3Malaysian Agriculture Research and Development Institute, 43400 Serdang, Selangor, Malaysia
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ABSTRACT
The extraction of pectin from a by-product of dragon fruit processing, was identified as an alternative source for commercial pectin. In this work, dried alcohol-insoluble residues (AIR) of dragon fruit peels were treated separately with ammonium oxalate/oxalic acid 0.25 %, pH 4.6, 85°C, HCl 0.03 M, pH 1.5, 85°C; and deionised water, 75°C. The pectin obtained from these methods were compared in term of yield, color, gelling characteristic and chemical structure. The highest yield for the extracted pectin from dragon fruit peels was 20.1 % (dry weight basis) by ammonium oxalate/oxalic acid extraction, contained 11.2 % moisture and 6.9 % ash. Extraction by deionised water yielded 15.4 % pectin, 11.3 % moisture and 11.6% ash. Whereas, the acid extraction gave the lowest yield 15 %), 11.1 % moisture and 12 % ash. The amount of pectin from all extraction conditions were comparable to pectin obtained from commercial apple (12 %) or citrus (25 %). Gelhardness test was performed for gelling properties measurement. The Fourier Transform Infrared Spectroscopy (FTIR) was useful in the identifying dragon fruit pectins. Different conditions used in the extraction do not show a difference in the pectin structure. With a good recovery yield and gelling properties, ammonium oxalate-extracted dragon fruit pectin present good characteristics to be exploited industrially as food additive.
ABSTRAK
Pengekstrakan pektin daripada sisa pemprosesan buah naga telah dikenalpasti sebagai sumber alternatif bagi pektin komersial. Dalam kajian ini, pepejal tak larut alkohol (AIR) kering daripada kulit buah naga diperlakukan secara berasingan dengan ammonium oksalat/asid oksalik 0.25 %, pH 4.6, 85°C; HCl 0.03 M, pH 1.5, 85°C; dan air ternyahion, 75°C. Pektin yang diperolehi melalui kaedah ini dibandingkan dari segi hasil, warna, ciri penggelan dan struktur kimia. Hasil pektin tertinggi daripada kulit buah naga ialah 20.1 % (berat kering) menggunakan ekstraksi ammonium oksalat/asid oksalik,mengandungi 11.2 % air dan 6.9 % abu. Ekstraksi menggunakan air ternyahion menghasilkan 15.4 % pektin, 11.3 % airdan 11.6 % abu. Manakala, ekstraksi asid memberikan hasil yang terendah (15 %), 11.1 % air dan 12 % abu. Pektin yang terhasil daripada semua keadaan pengekstrakan adalah setanding dengan pektin epal (12 %) atau sitrus (25 %) komersial.Ujian kekerasan gel dilakukan bagi mengukur sifat penggelan. Spektroskopi inframerah (FTIR) amat berguna bagi mengenalpasti pektin buah naga. Keadaan berbeza yang digunakan dalam pengekstrakan tidak menunjukkan perbezaan dalam struktur pektin. Dengan perolehan hasil serta ciri penggelan yang baik, pektin buah naga hasil pengekstrakan menggunakan ammonium oksalat/asid oksalik mempunyai ciri yang baik untuk diterokai secara industri sebagai bahan tambah makanan.
Key words: Dragon fruit; Pectin; Alcohol insoluble residue; Extraction conditions
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