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Low temperature preservation
- 1. M.Venkatasami, I.D.No: 2020641005 Ph.D.(Processing and Food Engineering) Department of Food Process Engineering AEC&RI, TNAU. LOW-TEMPERATURE PRESERVATION 7/16/2021 LOW-TEMPERATURE PRESERVATION 1
- 2. INTRODUCTION • Chilling isdefined by a storage temperature range between −1 and 8 ⁰C Chilling • Freezing refers to the storage of food at temperatures between −18 and −30⁰C. Freezing Reduces microbiological and biochemical spoilage Lower storage temperatures give a longer shelf life Little or no effect on the nutritional content or organoleptic properties of food Meat, fish, dairy products and chilled recipe dishes High-quality raw materials should be selected for freezing 7/16/2021 LOW-TEMPERATURE PRESERVATION 2
- 3. Cont. • Retention of organoleptic properties Advantages •Recrystallization • Vitamin loss • Oxidative rancidity Disadvantages Low temperature storage prevents, The growth of microorganisms Activity of enzymes Purely chemical reactions Shelf life Soft fruits 3 and 6 months at −12⁰C 24 months and beyond at −24⁰ C Meat 6–9 months at −12⁰ C 15 and 24 months at −24⁰ C 7/16/2021 LOW-TEMPERATURE PRESERVATION 3
- 4. FREEZING RATE ANDFREEZING POINT 7/16/2021 LOW-TEMPERATURE PRESERVATION 4
- 5. There isno clear freezing point of a food material water has a distinctive freezing point (0 ⁰C) For foods, the freezing range is normally between 0 and about −2 or −3⁰C. Cont. Three stages The removal of sensible heat from the food (Ti-Tf) The removal of the latent heat of fusion Sensible heat removal down to required storage temperature The freezing point is usually defined as the highest temperature at which ice crystals are found to be stable 7/16/2021 LOW-TEMPERATURE PRESERVATION 5
- 6. HEAT LOAD To calculatethe size of The freezing equipment Refrigeration circuit Two sensible heat Latent heat Heat load Δh = cpu (Ti − Tf) + λ + cpf (Tf − Tfinal) Assumption λ= the latent heat of water and the moisture content of the food Δh ϵ Ti and Tfinal 7/16/2021 LOW-TEMPERATURE PRESERVATION 6
- 7. 7/16/2021 LOW-TEMPERATURE PRESERVATION7 PREDICTION OF FREEZING TIME PLANK’S EQUATION
- 8. 7/16/2021 LOW-TEMPERATURE PRESERVATION8 Cont. NAGAOKA’S EQUATION STEFAN’S MODEL
- 9. SLOW FREEZING ANDRAPID FREEZING Schematic of rate of freezing on residence time of product in the critical zone 7/16/2021 LOW-TEMPERATURE PRESERVATION 9
- 10. Physical Properties ofFrozen Food Thermal diffusivity, α THE FROZEN STATE 𝑘 𝜌𝐶𝑝 𝝆𝒊𝒄𝒆 < 𝝆𝒘𝒂𝒕𝒆𝒓 𝝆𝒘𝒂𝒕𝒆𝒓 at 0 ⁰C = 999.8 kg m−3 𝝆𝒊𝒄𝒆 at 0 ⁰C= 920 kg m−3 𝝆𝒘𝒂𝒕𝒆𝒓 < 𝝆𝑼𝒏𝒇𝒓𝒐𝒛𝒆𝒏 𝒇𝒐𝒐𝒅 Proportion of frozen water increases ρ of frozen food falls, 10–15% T vs ρ 7/16/2021 LOW-TEMPERATURE PRESERVATION 10
- 11. Cont. 𝐶𝑝, decreaseson freezing 7/16/2021 LOW-TEMPERATURE PRESERVATION 11
- 12. Cont. k increaseson freezing, α independent of temperature, α, increases steeply as ‘T’ falls 7/16/2021 LOW-TEMPERATURE PRESERVATION 12
- 13. Commercial cold storesare held at about −25⁰C Domestic freezers normally operate at −18⁰C Constant low temperature should be maintained Fluctuations in freezer temperature give rise to the thawing Recrystallization of ice can result in a severe loss of quality Disruption to cell walls and a loss of texture FOOD QUALITY DURING FROZEN STORAGE 7/16/2021 LOW-TEMPERATURE PRESERVATION 13
- 14. Decrease in humiditygives rise to sublimation, Freezer burn, occurs at food with high surface area to volume ratio Results in discoloration and the denaturation of proteins Oxidative rancidity, sublimation increase the exposure of macromolecules to oxygen Sublethal injury(repairable) and lethal injury to microbial cells. Cont. 7/16/2021 LOW-TEMPERATURE PRESERVATION 14
- 15. 7/16/2021 LOW-TEMPERATURE PRESERVATION15 FOOD QUALITY DURING FROZEN STORAGE Psychrophile Temperature for growth: -5 to 20°C Optimum temperature for growth: 12 to 15 °C Refrigerated (0–7°C) foods Psychrotrophs Psychrotrophic microorganisms Temperature for growth: 2- 30°C Optimum temperature for growth: 20 to 30 °C Psychrotrophic bacteria of importance Pseudomonas
- 16. 7/16/2021 LOW-TEMPERATURE PRESERVATION16 Cont. Psychrotrophs BACTERIA Pseudomonas Cinetobacter Alcaligenes Flavobacterium MOLD Botrytis Cladosporium Geotrichum Mucor Penicillium Sporotrichum YEAST Candida Debaryomyces Rhodotorula Torulopsis FREEZING Prevents the growth of most foodborne microbes REFRIGERATION Slows down the growth of microbes
- 17. 7/16/2021 LOW-TEMPERATURE PRESERVATION17 Clostridium botulinum type E 3.3 °C Yersiniaent erocolitica 3 °C Salmonella spp. 4 °C Aeromonas hydrophila and Listeria monocytogenes <7 °C Monera, Penicillium, and Sporotrichum -4 °C Yeast -3 °C Refrigeration below 5°C effectively retards the growth of many foodborne pathogens Cont.
- 18. Humidity should bekept above 90% Reduce the movement of air across the stored product Frozen food should be glazed Layer of ice applied by a spray or by immersion, prior to freezing Protects food from sublimation Appropriate packaging Preventing freezer burn and reducing the risk of oxidative rancidity 7/16/2021 LOW-TEMPERATURE PRESERVATION 18 Cont. Good practices to minimize loss of quality
- 19. 7/16/2021 LOW-TEMPERATURE PRESERVATION19 FREEZING EQUIPMENT PLATE FREEZER T=−40⁰C Conduction mode Rectangular foods BLAST FREEZER All shapes and sizes >freezing time Batch, continues, spiral FLUIDIZED BED FREEZER T<−30⁰C IQF Rapid freezing rates SCRAPED SURFACE FREEZER Ice creams >−5⁰C Crystal growth CRYOGENIC FREEZER N₂ = −196⁰C CO₂=-78 ⁰C Batch & tunnel types IMMERSION FREEZER T<−21⁰C ,k (W/m²K) N₂, Salt brines Glycerol, glycol & CaCl₂
- 20. 7/16/2021 LOW-TEMPERATURE PRESERVATION20 THANK YOU