Preserveration - Lecture notes Perseveration 1 PDF

Preview

Summary

notes for preservation 1 and questions...

Description

What are the benefits of food preservation? Food is preserved with the shelf-life in mind. It offers increased food security via enhanced accessibility What is food spoilage? Changes in the composition of food resulting in appearance of unfavourable characteristics (qualitative) Types of spoilage Degradation of food inducing loss of organoleptic properties, nutrient loss and potential comprised safety (contamination) Physical spoilage Physical damage (microstructural) during harvest & processing (handling) of food products e.g., bruised fruit, packaging of chips (seal to prevent contamination). Chemical changes inducing changes in physical structure (physicochemical; loss of microstructure) e.g., separation of food with dispersion & suspension as their structure e.g., synthesis of water out of yogurt: moisture migration (change of glassy to rubbery state, crystal formation “enhanced rate of retrogradation”), moisture loss (dehydration of vegetables), and moisture gain (cake powders) Chemical spoilage Protein degradation in high protein food due to increased enzymatic activity (proteases), resulting in a liquefied pool of AA. (Fish has more proteases than meat), (UHT milk: protein denaturation forming a protein gel matrix). High fat food is more susceptible to lipid oxidation resulting in rancidity (qualitative). Polyphenol oxidase catalyses conversion of phenolic compounds to brown/black colour (qualitative) Microbiological spoilage Microbes (Bacteria, yeast & fungi) uses food as substrate for proliferation (qualitative degradation of food, loss of micro stability). Food borne pathogens comprises safety. Use-by-date (comprising safety “CCP”). Use-before-date (loss of quality “CP”). Pathogenic microorganisms Food borne pathogen (comprises safety, “easy to detect”). Fungi’s producing toxins e.g., mycotoxigenic fungi, Aspergillus (reduce aw), Penicillium. Viruses (hard to detect). Parasites (water borne) Foodborne illness Infections (via bacterial gut colonisation e.g., salmonella). Intoxications (via toxins produced by bacteria e.g., Bacillus cereus forming heat tolerant spores). Toxioinfections (via viable pathogens which produce toxins) Common spoilage microorganisms Bacteria (spore forming), Fungi (yeast & moulds) Factors controlling the rate and type of spoilage

Intrinsic factors Phenotype of food effected by aw, salt, sugar & polyols. Mechanical barrier (eggs, fruit), Antimicrobial substances, Redox reactions (oxidation) Extrinsic factors External environment influencing food via temperature & time, humidity (packaging), storage & processing conditions Processing factors Influence of processing operations on intrinsic & extrinsic factors (acidification, sterilization, pasteurization) Implicit factors Interactions between microorganism and host resulting in disease (characteristics of microorganism: tolerant to processing). (1) Bacteria, (2) Yeast, (3) Mould [favourable conditions]. [Stress conditions] tolerant microorganisms (slow growing mould) proliferation is enhanced due to decreased substrate availability. Dependant on ability to metabolise different substrates and tolerate stress (aw, osmotic pressure) Preservation vs quality: a balance, contest, or tension? Specific food-system, where aims it to optimise both principles (balance). The hurdle concepts Principle revolves around setting up multiple barriers (selection pressures) to microbial spoilage, application to intrinsic & extrinsic factors to spoilage. Requires a holistic approach considering if effects are additive, antagonistic, or synergistic Example: heat and pH Acidification 0.6 results in microbial growth during storage of food. Identification of microbes allow evaluation of specific aw required for proliferation Water activity (aw) Measures vapour pressure of food products and equalise to ambient vapour pressure, subsequently aw is measured. Dependant on addition of solutes. Relationship between water activity Food have specific aw. Aw can be reduced via (1) removed of water, (2) addition of humectants. Aw changes are dependent upon adsorption & desorption & temperature. AwStarch (polar group, high mw). Curing: Food products are salted (lowers aw) and dried e.g., meat. Brining: Food products laid in salt solution e.g., cheese Humectants: Sugar Variants of Food-Grade Humectants: Glycerol, Sorbitol, Propylene Glycerol [Provides taste & texture qualities]

pH control of microbial spoilage Specific pH for certain food microbes. 2.8pH (low pH bacteria: yogurt & cheese) 6.5-7.5pH (most bacteria) 9pH (high pH: protein rich food). Safe for consumption but may induce cross-contamination with external spores resulting in their proliferation which may results in mycotoxin formation Examples of the limiting microbial targets for differing pH ranges 4.6 (Requires further processing where use-by-date is marked). (2)(3) pH4.6 (presence of high aw results in spore forming bacteria which produce spores & toxins) Methods of Acidification Pickling (Fruit is cut and mixed with vinegar until ripen). Fermentation (Fermenting food from an unsafe to safe pH). Addition of acidity regulators (addition of organic acids) Putting pH and water activity together: Mayonnaise Acids may enhance flavour & aroma bounded by an optimal limit. pH63 “safe”...