Fundamental study on perspectives for post-harvest bioprotection of cereal crops

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Schmidt, Marcus
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University College Cork
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As a result of the rapidly growing human population, reducing post-harvest crop losses of cereals due to microbial pests has major importance. Therefore, recent advances and emerging technologies for chemical, physical and microbial grain decontamination were reviewed as part of this thesis. It became evident that no single treatment can sufficiently decontaminate cereals without quality deterioration. This thesis investigates the spread of a fungal contamination during storage if the crop is treated inappropriately. During 6 weeks of storage, the ergosterol content (measure of fungal bio-mass) increased from <0.75 ppm to 44 ppm. Substantial levels of mycotoxins, such as deoxynivalenol and zearalenone were found in concentrations up to 953 ppb and 78 ppb, respectively. Also the grain quality was reduced due to the degradation of carbohydrates and proteins by fungal hydrolytic enzymes. Consequently, the gluten quantity and network strength was substantially lowered, inducing dough and bread quality deterioration. This was particularly expressed by the increased dough stickiness, bake loss and open crumb structure. The optimisation of the antifungal performance of Lactobacillus reuteri R29 due to increased accumulation of phenyllactic acid (PLA) or reuterin was investigated also. While both compounds efficiently inhibited spore germination of Fusarium culmorum (106 spores/mL) in vitro, only PLA could successfully extend the microbial shelf-life of bread (4 days, 100%). Furthermore, emerging microbial, physical and chemical methods of decontamination, were investigated during cereal storage. While microwave (2 min, 800 W), microwave+NaOCl (5%), sorbate and propionate (both 5%, 10 min), high pressure (10 min, 300 MPa, 30°C) treatment and vacuum packing fully inhibited fungal growth and mycotoxin accumulation, ultrasound, quaternary ammonium compounds, cold plasma and LAB were not successful. However, the dry microwave treatment induced protein denaturation, resulting in poor quality of the resulting dough and breads. Finally, plant derived antimicrobial peptides were studied at the example of the cowpea-thionin II. After extraction and partial purification, the peptide was identified by N-terminal sequencing. The antifungal activity against 3 major food spoilage fungi (104 spores/mL) was shown. The extract was found to be resistant against heat treatment but lost its antifungal activity in presence of cations. Finally, it was successfully used to protect stored wheat grains from fungal spoilage. Overall, this thesis provides a valuable contribution to the knowledge regarding fungal spoilage and the possibilities and actual shortcomings of diverse emerging approaches and technologies for food preservation.
Cereal research , Antifungal agents , Bioprotection , Cereal storage
Schmidt, M. 2018. Fundamental study on perspectives for post-harvest bioprotection of cereal crops. PhD Thesis, University College Cork.