Penyakit simpanan pada gaplek yang disebabkan oleh aspergillus flavus

ORAMAHI, Hasan Ashari, Promotor Prof. Dr. Ir. Chistanti Sumardiyono, S.U

2008 | Disertasi |

Jamur marga Aspergillus sering ditemukan tumbuh pada gaplek. Salah satu spesies yang tumbuh dominan adalah A. flavus. Penelitian-penelitian yang mengungkap peran glukoamilase yang dihasilkan oleh A. flavus dalam menimbulkan kerusakan gaplek belum pernah dilakukan. Oleh karena itu, penelitian ini dilakukan untuk mengkaji peran aktivitas glukoamilase dari A. flavus dan pengaruh kondisi suhu dan lengas nisbi ruang penyimpanan terhadap kerusakan gaplek. Sampel gaplek diperoleh dari empat kecamatan di Kabupaten Gunungkidul yaitu Kecamatan Nglipar, Wonosari, Semanu, dan Rongkop. Pengambilan sampel didasarkan atas perbedaan tipe curah hujan. Kecamatan Nglipar dan Rongkop termasuk daerah tipe C3 dan Kecamatan Wonosari dan Semanu termasuk daerah tipe D3. Dari empat kecamatan tersebut diambil 4 sampel, terdiri atas gaplek petani 3 dan pedagang 1 sampel. Pengambilan sampel gaplek dilakukan secara acak. Isolasi jamur marga Aspergillus dari gaplek dilakukan pada medium DG-18. Biakan murni yang diperoleh (pada DG-18) dipindahkan ke cawan petri yang berisi medium CYA, CYA 20S, dan MEA untuk identifikasi dan penentuan dominasi spesies jamur Aspergillus. Percobaan in vitro bertujuan untuk mengetahui jamur marga Aspergillus penyebab kerusakan gaplek terbesar. Percobaan pengaruh lengas nisbi udara dan suhu ruang penyimpanan terhadap perkembangan A. flavus, aktivitas glukoamilase, dan kerusakan gaplek dilakukan selama 4 bulan. Rancangan percobaan yang digunakan adalah Rancangan Acak Kelompok (RAK). Parameter yang diamati adalah populasi A. flavus, bobot, aktivitas glukoamilase A. flavus, kadar air, kadar pati, dan kadar gula reduksi, dan granula pati gaplek. Granula pati diamati secara mikroskopis. Hasil identifikasi jamur marga Aspergillus dari gaplek yang diperoleh dari Gunungkidul didapatkan 6 spesies yaitu A. flavus, A. oryzae, A. niger, A. foetidus, A. tamarii, dan A. zonatus. Berdasarkan nilai indeks kekerapan relatif (relative index frequency, Rif) dan indeks kemunculan jamur (presence index of the fungus, Pif) dari keenam spesies tersebut, A. flavus merupakan jamur yang paling dominan dan penyebab kerusakan terbesar pada gaplek. Glukoamilase yang dihasilkan oleh A. flavus mampu mendegradasi pati menjadi glukosa sehingga aktivitas ini dapat digunakan sebagai indikator awal serangan jamur pada gaplek sebelum kerusakan secara fisik (warna jamur) tampak. Berdasarkan populasi A. flavus, bobot, granula pati, kadar air gaplek, aktivitas glukoamilase A. flavus, kadar pati, dan kadar gula reduksi gaplek dapat disimpulkan bahwa lengas nisbi udara 65%, suhu 30oC dan 35oC merupakan kondisi penyimpanan yang lebih baik karena populasi A. flavus lebih rendah dan kerusakan gaplek lebih kecil.

Among species of the genus Aspergillus, A. flavus is the most dominant species that grows on dried cassava. The role of glucoamylase produced by A. flavus in dried cassava deterioration has not been studied. Therefore, an in depth study focusing on storage disease on dried cassava caused by A. flavus needs to be conducted. This research was conducted to study the role of glucoamylase from A. flavus and the effect of temperature and relative humidity on the spoilage of dried cassava. Samples of dried cassava were obtained from four districts with different rain fall type. Nglipar and Rongkop were C3 type, while Wonosari and Semanu were D3 type. Four samples were taken from those four districts, three of them were from farmer and the other one were from seller. All of them were choosen randomly. Isolation of Aspergillus from dried cassava was done using DG-18 medium. The isolates were then cultured on petri dishes containing CYA, CYA 20S, and MEA media for identification and determination of dominant species. The in vitro experiment was to obtain the species of Aspergillus that is result in highest change of dried cassava spoilage. The effect of RH and storage room temperature to the development of A. flavus, glucoamylase activity, and spoilage of dried cassava was evaluated for 4 months using Randomized Completely Block Design. Variables observed were population of A. flavus, weight, glucoamylase activity, starch content, reduction sugar content, water content, and starch granule of dried cassava. Starch granule was observed microscopically. Identification showed there were six species of Aspergillus found i.e. A. flavus, A. oryzae, A. niger, A. foetidus, A. tamarii, and A. zonatus. Based on relative index frequency (Rif) and presence index of the fungus (Pif), A. flavus was the most dominant species and causing the highest deterioration on the dried cassava. Glucoamylase produced by A. flavus was capable of degrading starch to glucose so that this activity could be used as an early indicator of the infestation of dried cassava by the fungus. Based on the population of A. flavus, weight, water content of dried cassava, glucoamylase activity, starch content, reduction sugar content, and starch granule of dried cassava, it was concluded that RH 65%, the temperature of 30 and 35oC was better storage condition for dried cassava because it result in the lower population of A. flavus and deterioration of dried cassava.

Kata Kunci : Aspergillus flavus,Gaplek,Penyakit simpanan