食品保鲜学课件Chapter2antimicirobials2.pptVIP

Part I Food Ingredients Chapter 2Natural Antimicrobials Outline 2.1 Introduction 2.2 Antimicrobials from animal source 2.3 Antimicrobials from plant source 2.4 Antimicrobials from microbial source 2.5 Mechanism of Natural Antimicrobials --Summary 2.1 Introduction 2.1.1 Food Antimicrobials Definition Chemical compounds added to or present in foods that retard microbial growth or kill microorganisms Functions Inhibit or inactivate spoilage microorganisms pathogenic microorganisms Food safety problem 2.1.2 Why Natural Antimicrobials A number of compounds are approved Reasons of natural antimicrobials Expand the spectrum over the regulatory-approved substances Strict international regulation Green labels Limitations of Regulatory-Approved Substances pH limitation (Organic acid) Function @ pH 4.5-4.6 Few compounds effective @pH 5.5 Food component interactions Most food antimicrobials are amphilic Solubilize in or be bound by lipids or hydrophobic proteins Function @ lower pH pKa of regulatory-approved organic acids Regulatory-Approved Food Antimicrobials Natural sources for antimicrobials 2.1.3 Concern of Natural Antimicrobials Food safety effective, stable to storage and processes Standardized assays for activity needed Producers and users liable for claims Excellent but not miracle 2.2 2.2.1 Chitosan Natural constituent of fungal cell walls Produced commercially from chitin (by-product of shellfish processing) Structure Origin of Chitin Greek word Tunic/ envelope first isolated from mushroom in 1811 from the cuticles of insects in 1823 ? Commercial Chitosan Deacetylation: 35% High molecular weight cationic polysaccharide and tasteless fiber ? 1. Inhibition of bacteria Act mainly on the outer surface Positively charged Interact with the negatively charged bacterial cell membranes Lead to the leakage Interfere the normal metabolism Also acts as a chelating agent 2.Inhibition of Fungi Direct interference of fungal growth Activation of