Rarely, there may some hydrolytic rancidity associated with fats and moisture especially in alkaline conditions. This is in effect a soap formation.
In Biscuits, it is almost always caused by enzyme action, which means that ingredients that have not been heat-treated are involved, for example nuts in creams.
There are 3 types of rancidity:
1. Oxidative rancidity: Oxidative rancidity is associated with the degradation by oxygen in the air.Via a free radical process, the double bonds of an unsaturated fatty acid can undergo cleavage, releasing volatile aldehydes and ketones. Oxidation primarily occurs with unsaturated fats. The fat oxidation process, potentially resulting in rancidity, this chemical process continues slowly at lower temperature.Thus, airtight packaging will slow rancidity development.
2. Hydrolytic rancidity: Hydrolytic rancidity refers to the odor that develops when triglycerides are hydrolyzed and free fatty acids are released.This reaction of lipid with water sometimes requires a catalyst, but results in the formation of free fatty acids and salts of free fatty acids. In particular, short-chain fatty acids, such as common butter fats, are odorous. Rancidity in foods may be very slight, indicated by a loss of freshness to very severe, indicated by objectionable odors and/or flavors.
3. Microbiological rancidity: Microbial rancidity refers to a process in which microorganisms, such as bacteria or molds, use their enzymes such as lipases to break down fat.
Things that Directly affecting to the rancidity in biscuits:
2. Raw Materials Handling Conditions
3. Finished products handling Methods
Raw Materials that can be prone to be rancid faster in the biscuits industry
1. Oil Bulk -There are some handling conditions accelerate oxidative changes, which produce rancidity tastes and smells. For example, when handling fats warm and in bulk, agitation that promotes the inclusion of air (oxygen), which will accelerate the oxidative rancidity .
2. Oil Box Fat - Fat delivered in boxes in plastic bags. If handling has been, rough these bags may be damaged and some fat may leak out and become absorbed into the cardboard of the boxes. This is obvious and if possible,as the fat in the cardboard will rapidly become rancid. This rancid fat will accelerate the deterioration of the rest of the fat in that box.
3. Cream Fat - Biscuit cream fats have higher solid fat indices at ambient temperatures than dough fats. They are thus either hydrogenated fats or fats based on Lauric fats (coconut and palm kernel oils).These fat are much less likely to develop rancidity
4. Flour - Flour is normally at about 14% moisture. It is therefore prone to mold growth & infestation by insects and larger animals. Flour ages after milling, and the effect of the ageing is to cause the gluten to become a little stronger that is less extensible and more elastic. Both conditions are less desirable for most biscuits. Old flour may also become rancid and therefore taste unpleasant.
5. Full cream Milk Powder - its mostly oxidative rancidity
6. Desiccated Coconut & Nuts - Coconut oil is very resistant to rancidity in dry conditions. Therefore, desiccated coconut may be stored for many months but advised to used roasted desiccated coconut by contrast, the fat in other types of nuts is very prone to oxidative rancidity even after roasting, and should be checked accordingly
How Raw Materials Handling Conditions & Using Conditions affecting to fat Rancidity & How to overcome
Oil Bulk: There are some handling conditions accelerate oxidative changes, which produce rancidity tastes and smells. For example, when handling fats warm and in bulk, agitation that promotes the inclusion of air (oxygen) should be avoided.All containers, pipework and valves must be free from heavy metals, particularly copper. Therefore, no brass fittings should ever be exposed to fats, as these metals act as catalysts for the oxidation process.
Oil Box Fat: Box Fat delivered in boxes in plastic bags. If handling has been, rough these bags may be damaged and some fat may leak out and become absorbed into the cardboard of the boxes. This is obvious and if possible, boxes in this condition should not be accepted. If this is inevitable, any fat in damaged boxes should be used immediately, as the fat in the cardboard will rapidly become rancid. This rancid fat will accelerate the deterioration of the rest of the fat in that box.
Flour: Should be stored in cool dry conditions, used strictly in stock rotation and kept for minimum periods, Flour can easily pick up taints, so storage of bags and sacks should be well away from strong smelling materials such as spices and detergents. Check that your flour supplier has an entoleterand that they used it in the final step of flour production before bagging. That system effectively breaks any insect eggs, which may have been picked up from places in the mill. Flour silos should be insulated to reduce temperature fluctuations due to weather conditions. If the walls are allowed to cycle strongly in temperature, migration of moisture within the flour may cause lumping and adhesion to the silo walls. Silos should be emptied completely before refilling, and occasionally they should be cleaned down to remove all traces of material that hangs in corners or in the top surfaces of the silo. If these are not cleared, they become hard, rancid and may be infested.
How unpacked Biscuits prone to rancid if not following the correct procedures
In many cases, baked and satisfactory biscuits are not wrapped directly after they have been baked and cooled. This may be because there is a fault at the wrapping machine or because the biscuits are to be subject to some secondary process that cannot be an in-line operation. In all these cases, the biscuits must be manually transferred into storage boxes. The plastics box (Crates) should have lids which fit tightly or they should stack well to protect the contents from exposure to the air, see below.
Filled boxes should be lidded or stacked in a way that protects the contents from exposure to the atmosphere. This is because biscuits pick up moisture very quickly from the air and become soft and much more prone to fat rancidity. If lidding is not possible, the filled boxes should be stored in a room at a relative humidity of less than 30%. The temperature of this storage room is not as important as the relative humidity.
Boxes should be cleaned thoroughly regularly and any loose crumbs taken out before new biscuits are placed in them. Old crumbs are a source of fat rancidity, flavour or colour contamination.
How can rancidity be controlled
1. Proper Handling of raw Materials as mentioned above
2. Proper handling of post baking operation ( Unpacked biscuits ) such as collecting to the plastics crates
3. Cleaning and hygienic conditions of the utensils ( Maintain Proper cleaning programs)
4. Cleaning of the Mould after production with hot water reaming dough will generate fat rancidity .
Attention has been drawn to the potential problems of fat rancidity on biscuit quality. Precautions have been listed to reduce the incidence of rancidity. In fact, precautions will not prevent rancidity occurring they will merely slow the onset. It is not unusual to use chemicals known as antioxidants to slow the onset of rancidity. For maximum effectiveness, these should be added by the fat refiner immediately after the end of the process.
There is a range of antioxidant materials, and all are strictly controlled by food legislation. They are rather unpleasant chemicals. If fats are handled correctly, the use of antioxidants offers little advantage.They may be useful if the fat bulk handling facilities or the biscuit packaging systems are poor.
Correct Packaging Vs Rancidity
Many factors can affect the tendency of an oil to become rancid. The first is too much exposure to air. Since oxidative rancidity is the most likely kind of rancidity to affect biscuits so the biscuits must be packed properly with correct materials , must have to check the air leakage every , minute in online process .
The barrier, which prevents moisture pick up by the biscuits from the atmosphere, will also be adequate for hygiene aspects. Plastic (polypropylene), plastic coated papers, or various laminates can be used to form the moisture barrier. They are usually heat sealable and this is how the pack is closed on the wrapping machine. The barrier properties are a combination of the basic moisture proofness of the materials used and the effectiveness of the seals. Tests for moisture proofness form a significant part of shelf life testing.
The Next factors are heat and light. Since both of these factors can also speed up the rancidity process, protection from heat and light are also important when it comes to biscuits .With respect to light packaging materials must have UV barriers.
Biscuits must store in cool and dry place as heat will accelerated the oxidative rancidity .