Oxidation + membrane filtration
a lot of bright but unfocused thinking. The practical result of this is that more than 90% of all A. barbadensis material processed is pasteurized.
Differing forms of pasteurization remain at the heart of the intermediate processing of aloe. From here on we will consider bacteria alone because mold-laden aloe should not be allowed into the processing plant. When moldy aloe is encountered, the material should be removed with minimal agitation from the area and the manufacturing environment immediately sanitized. Under no circumstances should an attempt be made to process fungally-contaminated aloe. Even killing the vegetative forms does not destroy the spores.
Batch pasteurization in unsealed kettles is the traditional method for reducing bacterial numbers (Figure 8.5, Process J). Usually 100 to 2,000 gallons (400 to 8,000 liters) are fed into a steam-jacketed, electrically-heated or gas-fired kettle and the temperature raised to 65 °C (150 °F). Attaining this temperature can take from 15 to 60 minutes depending on the equipment used in the processing facility. In standard pasteurization the material is then held at 65 °C for 15 minutes. With smaller batches the material is then allowed to cool to near ambient by radiation and/or convection. With larger batches, heat exchangers are usually employed to more rapidly reduce the temperature of the gel to the point where it can be further managed. During these processes the kettle is covered, although no attempt is made to exclude oxygen. Sweep agitation is employed in order to speed both the heating and cooling phases. Often decolorization, activated by adsorbtion on charcoal, is performed after the heat is turned off and cooling begins.
However, it is not often that processors intelligently use bacteriology to set the parameters for pasteurization prior to a processing run and the subsequent bacterial quality control. There is insufficient time between the arrival of the gel at the processing plant, and the initiation of intermediate processing to allow for prospective bacteriology. However, if raw gel is routinely cultured quantitatively and a profile of incoming raw material established, then pasteurization can be adjusted to the average and expected bacterial content of the incoming gel. In reality a temperature of 65 °C is seldom used by the industry because it is rare for commercial raw aloe to have less than 100,000 CFU/ml. Even moderately high concentrations of organisms (106/ml) can result in insufficient pasteurization under standard conditions (65 °C, 15 minutes). Many companies therefore employ prolonged pasteurization times and elevated temperatures in unsealed kettles in order to ensure the complete killing of bacteria. The results of this will be discussed in the following section.
The numbers of bacteria in Whole Leaf Extracts are so high (minimum observed in raw extract >35,000CFU/ml, usually 500,000CFU/ml), that standard pasteurization conditions are likely to fail. This is because heat kills a fixed percentage of organisms per unit time and temperature ('the kill curve'). The kill curves are different for different organisms depending on their heat sensitivity. The 'staph' and 'strep' found on human skin and hair have a so-called 'usual' degree of thermal sensitivity and in fact this is how 'usual' is defined. The micrococci are killed less readily by heat than is 'usual' and the aloe-associated Gram —ve rods are killed more readily. However, if a treatment is 99.99% effective in killing, it will sterilize a solution with 103 CFU/ml but it will be ineffective on a solution of 106CFU/ml, as 100 organisms will survive. If an organism is less heat tolerant than the average (e.g. the aloe-associated Gram —ve rods) the above treatment will kill 99.9999% of the heat-sensitive organisms and a solution with 105 CFU/ml will be sterilized. On the other hand, a heat tolerant organism (e.g. the aloe-associated micrococci) will only suffer a 99% decrease in numbers and bacterial breakthrough may occur in materials with initial counts of 103 CFU/ml. In order to reliably process Whole Leaf Extracts with bacterial counts that can routinely exceed 106 heat-tolerant micrococcal CFU/ml, a kill ratio of 99.9999% must be achieved. This cannot be done at 65 °C with 15 minutes treatment.
Due to the limitations alluded to above, larger and more modern processing plants are employing high-temperature/short-time (HTST) pasteurization (Figure 8.6, Process K). This sealed but non-pressurized system employs a series of heat exchangers to rapidly-within seconds-raise and then lower the temperature of the liquids. In the regeneration cycle, product entering the HTST unit is initially heated in the first stage of the exchanger by product leaving the HTST. It then passes through a heater section where its temperature is raised to 90—95 °C and then proceeds into a set of holding coils where pasteurization occurs. The duration of pasteurization is determined by the length of the coil and the flow rate. Typical pasteurization times are between one to five minutes. The pasteurized product then re-enters the regenerating heat exchanger
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