1/17/2016 Desiccation Osmotic Pressure Use of high concentrations of sugar or salt to Gradual removal of water from cells leads to preserve food is based on the effects of osmotic metabolic inhibition pressure. Not an effective microbial control as many cells A hypertonic environment retain ability to grow when water is reintroduced is created that causes water Lyophilization-freeze drying method used to preserve bacteria Bacteriostatic for some bacteria as the bacteria Used in curing of meats and to preserve fruits cannot grow or reproduce but many remain viable Viruses and bacterial endospores are resistant to Molds and yeast are able to grow on materials under osmotic pressure.This combined with their desiccation. ability to grow at lower pH is why molds and yeast may be the cause of fruit spoilage. Radiation Ionizing Radiation Radiation has various effects on cells depending on its wavelength,intensity,and duration. Ionizing radiation-short-wave length of radiant Radiation that kills microbes is of two types: energy gives deep penetrating power that has ionizing and nonionizing radiation sufficient energy to cause ionization of water forming highly reactive hydroxyl radicals, which are particularly damaging to DNA Radiant Energy gamma rays,X-rays,cathode rays Spectrum -used to sterilize heat sensitive materials, such as medical supplies(suture material) and food products(vitamins,herbs) 1/17/2016 9 Desiccation • Gradual removal of water from cells leads to metabolic inhibition • Not an effective microbial control as many cells retain ability to grow when water is reintroduced • Lyophilization – freeze drying method used to preserve bacteria • B ct i st tic B acteriost atic f s m b ct i s th b ct i for som e b acteria as th e b acteria cannot grow or reproduce but many remain viable • Viruses and bacterial endospores are resistant to desiccation. Osmotic Pressure • Use of high concentrations of sugar or salt to preserve food is based on the effects of osmotic pressure. • A hypertonic environment is created that causes water to leave the microbial cell inhibiting growth. • Used in curing of meats and to f preserve fruits • Molds and yeast are able to grow on materials under osmotic pressure. This combined with their ability to grow at lower pH is why molds and yeast may be the cause of fruit spoilage. Radiation • Radiation has various effects on cells depending on its wavelength, intensity, and duration. • Radiation that kills microbes is of two types: ionizing and nonionizing radiation Radiant Energy Spectrum Ionizing radiation – short-wave length of radiant energy gives deep penetrating power that has ffi i i i i f Ionizing Radiation sufficient energy to cause ionization of water forming highly reactive hydroxyl radicals, which are particularly damaging to DNA - gamma rays, X-rays, cathode rays - used to sterilize heat sensitive materials used to sterilize heat sensitive materials, such as medical supplies (suture material) and food products (vitamins, herbs)