Main characteristics of fats and oils commonly used in bakery products

Soybean oil: Soybean oil is often used as the raw material for frying products and margarine, and its fatty acid composition accounts for more than 80% of unsaturated fatty acid. It is characterized as containing 8.3% of highly unsaturated fatty acids (linoleic acid), so it has a fishy smell. For this reason, a small amount of hydrogenation is used to make a product with a composition similar to that of cottonseed oil.

Palm oil: Palm oil is the oil obtained from the fruit of the oil palm tree. Palm oil can be extracted from the pulp and palm kernel oil from the seed kernel. In the fatty acid composition of palm oil, the unsaturated fatty acid is 50%-60%, which is less than other vegetable oils. Moreover, there are more oleic acid in unsaturated fatty acids and more soft fatty acids (palmitic acid) in saturated fatty acids, accounting for about 45%, so it has good stability and is a semi-solid vegetable fat with a melting point of 30-40°C. If it is in a semi-molten state, palm oil can be extracted from the pulp and the seed kernel.

If palm oil is left in a semi-molten state for a period of time, the lower layer will form solid fat and the upper layer will form liquid oil. The upper layer of oil can be separated for frying, the lower layer of slightly soft solid can be used as shortening, and the harder one can be used as hard butter (Hard Butter), which is often used to replace cocoa butter and is the raw material of chocolate.

Butter (Butter Fat): Butter, also known as cream, is the fat separated from cow’s milk, with the following characteristics:

1, contains a variety of fatty acids;

2, saturated fatty acids in the soft fatty acid content is the most, also contains only 4 carbon atoms of butyric acid (Butyric Acid C4) and other volatile fatty acids;

3, unsaturated fatty acids to the most oleic acid, linoleic acid less (1.3%);

4, melting point 31-36 ℃, good melting in the mouth;

5, contains a variety of vitamins; lutein is the main pigment that makes it yellow, but its cholesterol content often makes consumers wary;

6, diacetyl and other hydroxyl compounds so that it has a unique flavor. Because of the above characteristics, it is not only a good raw material in high-grade bread, cookies, cakes, but also often used as a benchmark for solid fats and oils.

Lard: Lard is the fat around the back and belly subcutaneous fat and internal organs of pigs, refined by refining, decoloration, deodorization and deacidification. The fatty acids of lard are characterized by an odd number of carbon atoms, and lard can be effectively identified according to this feature. The unsaturated fatty acids of lard account for more than half, mostly oleic acid and linoleic acid, and the saturated fatty acids are mostly palmitic acid. Lard melting point is low, plate oil of 28-30 ℃, the kidney part of the fat, the best quality, melting point 35-40 ℃, so in the mouth easy to melt, so that people feel cool and refreshing. The shortening of lard is better, but the fusion is slightly worse, and the stability is not good. Therefore, it is often used to lighten or cross ester reaction treatment to improve the quality of lard.

Shortening: shortening is generally animal and vegetable oils processed by refining or hardening, mixing, quick-cooling, kneading and other treatments so that it has plasticity, emulsification and other processing properties of fats and oils. It is generally not directly consumed, but as a raw material for food processing.

Shortening is divided into hybrid and hydrogenated types. Mixed shortening because of more vegetable oil, more susceptible to oxidation rancidity, its antioxidant index AOM (ActiveOxygen Method) common about 40h, a little only 16-18h. But because of the plasticity, consistency is good, the price is cheap, it is commonly used in the production of confectionery, bread and so on.

Hydrogenated shortening is generally hydrogenated with a single vegetable oil (cottonseed oil, soybean oil), etc. This hydrogenation method of shortening is very qualitatively good compared to the same consistency of the oil obtained by the mixed method, with an AOM of more than 70. If you mix two or more hydrogenated oils, you can get not only good stability and a wide range of plasticity of the shortening, cookies and fried products, it is best to use this hydrogenated shortening.

Margarine: edible animal and vegetable fats and oils and hydrogenated, fractionated, esterified fats and oils in a mixture of one or more kinds of fats and oils as the main raw material, with or without the addition of water and other auxiliary materials, by emulsification, frozen or not by the sharp cold kneading and made of a similar characteristics of the natural cream of the plasticity or fluidity of the edible fats and oils products.

Chemical properties of fats and oils affecting the shelf life of food products

I. Hydrolysis

Fats and oils can be hydrolyzed with water and decomposed into fatty acids and glycerol. Hydrolysis of fats and oils occurs during the frying operation, the rise in temperature, the presence of acid, alkali, enzymes can promote the hydrolysis of fats and oils. Saponification also occurs in the presence of alkali. Two important indicators for the determination of fats and oils are the SaponificationValue SV and Acid Value AV.

Saponification value refers to the mass of potassium hydroxide (KOH) required to saponify all fatty acids (including free fatty acids and combined fatty acids) in 1g of fat (mg), which is an indicator for identifying the purity and decomposition of fats and oils.

The acid value of fats and oils is expressed by the mass of KOH (mg) needed to neutralize the free fatty acids in 1g of fat. According to the change of acid value, it can be deduced that the stability of the storage of fats and oils. Generally fresh fats and oils, acid value in 0.05-0.07.

Second, the rancidity of fats and oils

Fats and oils or oil content of more food, during storage, due to the role of oxygen in the air, sunlight, microorganisms, enzymes, water, etc., the stability of the oil molecules gradually oxidation and hydrolysis, resulting in low molecular degradation of fats and oils degradation products and thus the occurrence of unpleasant odors, tastes bitter, and even has a toxicity. This phenomenon is fat rancidity, commonly known as fat ha defeat.

(A) Hydrolyzed rancidity

Containing more low-grade fatty acids in the oil, the residue of esterase or contamination of microorganisms produced by esterase, under the action of the enzyme, hydrolysis of fats and oils to generate free low-grade fatty acids (containing C10 or less), glycerol, monoacyl or diacylglycerol. The short-chain fatty acids (butyric acid, acid, octanoic acid, etc.) have a special odor of sweat and bitter taste, so that the oils and fats produce rancidity odor. This phenomenon is called hydrolytic rancidity of fats and oils. The hydrolysis of fats and oils to generate free fatty acids, will not produce an unpleasant odor. For example, butter (cream) in the hydrolysis of caseinate on the odor, the main reason for this effect is the presence of lipase, but this phenomenon is not rare in advanced fatty acids.

(ii) keto rancidity (β-type oxidative rancidity)

Hydrolysis of oils and fats produced free saturated fatty acids, in a series of enzyme-catalyzed oxidation of keto acids and methyl ketone with a strange smell, known as ketone-type rancidity. Due to the degradation caused by oxidation, mostly occurring in the saturated fatty acids between the α and β carbons on the Jian, so called β-oxidation.

General water and protein-containing oil-containing foods or fats are susceptible to microbial contamination, resulting in hydrolysis-type rancidity and β-type rancidity. The way to prevent the above two kinds of rancidity is in the processing of fats and oils, improve the purity of fats and oils, reduce the content of impurities and moisture, packaging containers must be dry and clean to avoid contamination, and storage at lower temperatures.

(iii) Oxidative rancidity (automatic oxidation of fats and oils)

Unsaturated fatty acids in fats and oils exposed to air, easy to occur automatically oxidized, decomposed to produce low-grade fatty acids, aldehydes and ketones, resulting in bad odor and taste bitter phenomenon, known as oxidative rancidity of fats and oils. Automatic oxidation of fats and oils is the main phenomenon of deterioration of fats and oils and foods containing fats and oils. This type of rancidity occurs mainly in fats and oils with a high content of unsaturated fatty acids, such as soybean oil, corn oil, olive oil, cottonseed oil and other fats and oils.

Enzymes, sunlight, microorganisms, oxygen, temperature, the influence of metal ions, can make the rancidity accelerated, hydrolysis is also the main factor to promote rancidity. From the basic situation of the above fats and oils can be seen in the structural composition and characteristics of butter, and in the product application of the actual situation there will be what problem? Here we look at a real case:

Actual case

A large enterprise to a large store production butter soufflé, the beginning of the product is very best-selling, three months after the emergence of consumer complaints about product odor, and later found that each batch of product odor, product odor over time is more and more obvious, had to stop production to find out why:

Product formula: wheat flour, salted duck egg yolk (≥ 15%), sugar, water, red beans, butter (≥ 6.8%), maltose, vegetable oil, food additives (acetylated diastarch phosphate, glycerol, sodium polyacrylate, sorbitol, sodium caseinate, mono-, di-glycerol fatty acid esters, sodium amylopectin octenyl succinate, glucono – α- lactone, β-carotene, potassium sorbate, sodium dehydroacetate), glucose syrup, sodium dehydroacetate ), glucose syrup, alginate, fresh egg, glutinous rice flour, shortening, sesame, white wine, edible salt, edible alcohol, starch.

Product packaging: the product is packaged in an independent form, the package is placed in the deoxidizer, the plastic film for the K nylon composite film, there is a barrier to oxygen, independently packaged products in the shelf life in an oxygen-free state.

Taste: sour smell, taste like cheese, not oil oxidation oil ha taste.

The center temperature of the product after baking :82-83℃.

Product physical and chemical indicators, microbiological testing:

Product moisture test: 14%

Physicochemical test: acid value 6.7mgKOH/g, peroxide value 0.01%.

Product microbiological test: total number of colonies 80cfu/g, coliform <10cfu/g

In summary: the product tastes bad initially exclude the fat is oxidized and rancidity, do not rule out the possibility of hydrolysis of fats and oils due to rancidity.

Reasons for hydrolysis of oil and grease in the product.

(1) The product may be contaminated by microorganisms and caused by hydrolysis of fats and oils deterioration, through the above product micro-objects detection, the product microorganisms are qualified, it can be judged that the product flavor after packaging is not caused by microbial contamination.

(2) Butter in the process of thawing time is longer and thawing method may cause butter deterioration and flavor, can be tested by comparing the experiments to see if the butter thawing method caused by deterioration.

(3) Whether the raw materials contain lipase, caused by lipase hydrolysis of fats and oils leading to product deterioration, bakery product materials generally may contain lipase materials such as wheat flour, improver, can be excluded from the raw material label and comparative experiments for testing and analysis.

After the experiment, natural butter in the long shelf life of bakery products freshness problem solutions are as follows:

(1) the need to use fresh butter raw materials, procurement of freshness (shelf life of no more than half) better butter, and according to the storage requirements of the product package labeling (-18 ℃ freezer) storage, use according to the requirements of the thawing method of thawing in a timely manner after use.

(2) products in the formula design to avoid the use of lipase monomer or compound improver containing lipase, especially high moisture products, such as bread, cakes, soufflés and other pastries.

(3) The use of raw materials to avoid bringing in lipase, with the development and application of enzyme promotion, some flour millers in the special flour added lipase to increase the functional properties of the product and improve the economic benefits of the product. Therefore, add butter to the baking products should be selected does not contain lipase wheat flour.

(4) The packaging of the product should be made of poorly permeable packaging film/bag (with K coating or aluminized film), the seal of the package should be well sealed (no air leakage), nitrogen can be used to fill and release the oxygen in the package, or vacuum packaging, and the package can be added with deoxidizer if the cost is acceptable.

(5) In the case of meeting the process conditions, baking temperature as high as possible or longer baking time, in order to fully inactivate microorganisms and enzymes.

(6) The product should be stored in a low temperature, dry, cool place for storage, avoid storage at high temperature for a long time.