Effects of square waveform pulsed ohmic heating on the vegetative cells and spores of B. cereus and Clostridium spp in the biogas digestate

Abstract

In this work, microbial inactivation experiments are performed on the biogas digestate samples via laboratory type ohmic heating system. The ohmic heating system ensures 2.72 V/cm voltage gradient with 50 Hz frequency square waveform pulsed alternating signals. Operations with 5 min and 15 min holding times are carried out at 70°C target temperature. Microbiological analysis performed before and after ohmic heating treatments with 5 minutes holding times revealed that, the number of Clostridium spp spores and vegetative cells suspended in the digestate with the related composition, are subjected to log reduction as 0.987 and 1.650 respectively. As a result of the 15 minutes holding time, it is determined that Clostridium spp spores and vegetative cells exhibited log reductions 0.819 and 1.725 respectively. The ohmic heating operation with 5 minutes holding time resulted in 18% decrease in the number of B.cereus spores and 55% increase in their vegetative cells in the same product. As a result of the 15 minutes holding time, the number of B.cereus spores and the vegetative cells increased by 37% and 23% respectively. Existing literature work on ohmic heating generally discusses the effects of the process parameters on the inactivation of microbial species which exist in various food matrixes. In this work, the effect of ohmic heating on the microbial inactivation of the biogas digestate which is originated from a biogas plant utilizing chicken manure as a substrate is investigated.

Keywords

• Ohmic Heating
• Pulsed Ohmic Heating
• Square Waveform
• Microbial Inactivation
• Biogas Digestate

Kare vurgu dalgalı ohmik ısıtma işleminin, biyogaz prosesinden elde edilen fermente ürün içerisindeki B. Cereus ve Clostridium spp türlerinin canlı hücre ve sporları üzerindeki etkileri

Öz

Bu çalışmada, laboratuvar tipi ohmik ısıtma sistemi kullanılarak biyogaz santralinden alınan fermente ürün örneği üzerinde mikrobiyolojik inaktivasyon denemeleri gerçekleştirilmiştir. Ohmik ısıtma işleminde 50 Hz frekansında, 2.72 V/cm voltaj gradyanı sağlanan kare vurgu dalgalı alternatif sinyal kullanılmıştır. 70°C hedef sıcaklıkta, 5 dk ve 15 dk bekleme süreli işlemler gerçekleştirilmiştir. 5 dk bekleme süreli ohmik ısıtma işlemlerinin öncesi ve sonrasında gerçekleştirilen mikrobiyolojik analizler, ilgili bileşimdeki fermente ürün içerisindeki Clostridium spp spor ve canlı hücrelerinin sırasıyla 0.987 ve 1.650 log azalmaya tabi olduğunu göstermiştir. 15 dk bekleme süreli işlem neticesinde Clostridium spp spor ve canlı hücrelerinde sırasıyla 0.819 ve 1.725 log azalma tespit edilmiştir. 5 dk bekleme süreli ohmik ısıtma uygulaması neticesinde, aynı ürün içerisinde yer alan B.cereus spor sayısında %18 azalma, canlı hücre sayısında ise %55 artma tespit edilmiştir. 15 dk bekleme süreli işlem neticesinde B.cereus spor ve canlı hücre sayılarında sırasıyla %37 ve %23 artış meydana gelmiştir. Ohmik ısıtma kapsamındaki mevcut literatür çalışmaları genellikle, uygulanan proses parametrelerinin, çeşitli gıda ürünü matriksleri içerisinde bulunan mikrobiyal türlerin inaktivasyonu üzerine olan etkilerini tartışmaktadır. Bu çalışmada, ohmik ısıtma işleminin, proses girdisi tavuk gübresi olan bir biyogaz santralinden elde edilen fermente ürünün mikrobiyal inaktivasyonu üzerine olan etkisi araştırılmıştır.

Anahtar Kelimeler

• Ohmik Isıtma
• Vurgulu Ohmik Isıtma
• Kare Dalga
• Mikrobiyal İnaktivasyon
• Biyogaz Digestat

Kaynakça

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