Different varieties of pulses can be fried in oil to manufacture a range of alternative snack products. It is essential that manufacturers not only have the right equipment to do this properly and safely, but also the technical know-how to produce the highest quality product with that equipment. The processes and supporting technology involved in frying pulses is also critical, whether you’re producing fried peas, fried chickpeas, or fried lentils.
Peas are rehydrated in water with sodium bicarbonate that is held at room temperature for 8 – 10 hours. The soak time is critical as oversoaked peas tend to produce a higher level of fines (i.e., small legume pieces freed during processing) and their skins are removed more easily during the cooking process. Oversoaking will also lead to pea fermentation, rendering them unusable by the manufacturer. Product quality can also be seriously compromised if the peas are allowed to rupture.
Temperature during soaking is important. Too high a temperature will cause the starch within the peas to gelatinize and the protein to denature (i.e., to undergo structural changes that diminishes or eliminate functional properties). During the soaking step, the moisture content of the peas increases up to 57 %, while expanding the peas to approximately twice their original size. Peas soaked in sodium bicarbonate also have a lower bulk density. One of the main reasons for using sodium bicarbonate is to trigger a reaction with the acid in the pea. A hydrogen ion from the pea that reacts with a bicarbonate ion, carbon dioxide is then released, thus expanding the peas.
Changes in Coloration
Adding the sodium bicarbonate during soaking affect the color of peas. By initially increasing the pH of the soak water (sodium bicarbonate is a mild alkali), it reacts with the chlorophyll to enhance the pigments within the pea. The phytyl and methyl groups are displaced and bright green water-soluble chlorophyllin is formed. The sodium salts of chlorophyllin give the soaked peas their bright green coloration. Even greater brightness is achieved with the addition of green food coloring in the soak water. Increasing the pH of the water ensures that the water absorbed into the pea will have a higher pH once dehydrated. In this way, it also alters the normally intense blue coloration of the dried pea.
Once the peas have been soaked, they must be fried to reduce the moisture content below 2.5 %. A fryer designed specifically for frying green peas is preferred. Ideally it should include a single frying pan that holds oil and controls the temperature profile of the oil throughout the fryer. The flexibility to vary the temperature of the frying oil can help improve the product quality of the peas. The quality tends to be better when employing a frying system that uses a lower temperature at the start of the frying process and a higher temperature near the end. Peas are sensitive to high temperatures. Using a fryer that can control the temperature profile is, therefore, crucial to maximizing quality. Toward that end, considerable attention is paid to the rate at which the fryer temperature increases as this is necessary to ensure that the final moisture content is acceptable. A temperature increase that is too slow will result in a final moisture content that is too high. This temperature profile produces no surface blistering and less expansion of the pea skin. Peas placed directly into oil at 356 °F (180 °C) experience surface blistering and greater expansion of the skin surrounding the peas. Submerging the peas at too high a temperature in the critical early part of the process causes the skin to be dislodged and the cotyledon to be expelled into the oil. Too low a temperature will lower the output, lengthen the fry time, and increase the oil absorption. The best products are those produced via a frying system that is able to leverage both quality and throughput. The sodium bicarbonate serves several critical function during frying. These include softening the texture and production of carbon dioxide that occurs at temperatures over 248 °F (120 °C). When the peas are fried, lighter texture and better mouthfeel are produced
Changes in Coloration During Frying
The bright green coloration of the pea developed during soaking will change during frying due to cell disruption. The high frying temperatures causes cells to swell and break in some cases. The contents of cells (including organic acids) escape from the vacuoles (i.e., a membrane bound cavity within a cell) into the inter cellular spaces and into the oil. As the acid contact increases, the chlorophylls change in such a way that the yellow and orange pigments within the peas are made visible along with the intense green chlorophyll. This combination also generates pheophytin which is olive green, providing peas an olive-green appearance, a color they will retain even after being fried unless artificial green coloring was added to the soak water.
Oil Deterioration During Frying
Managing and minimizing oil deterioration is an important part of promoting the highest quality fried pulses. A number of different elements contribute to the deterioration of the frying oil, including UV light, certain metals (e.g., copper), water, and oxygen. These catalysts should, therefore, have limited contact with the oil. For a product like fried peas, it is fairly difficultto minimize the contact with water as it is necessary to remove a large quantity of the water present in the peas during the frying process. A good filtration system and the correct frying parameters will help minimize deterioration.
The life of the oil can be further extended by keeping the level of fines to a minimum during frying; this practice also promotes a better yield and higher quality. Those fines that find their way into the frying oil will remain unless filtered out or removed via a sludge removal conveyer. If they are allowed to accumulate it will cause hydrolysis (i.e., chemical decomposition brought on by reacting with water) of the oil. The oil can be protected if the processor is able to adjust the temperature profile during the frying process. This helps minimize the level of fines produced from ruptured cotyledons or skins being removed from the peas.
Chemical, Physical, and Structural Changes during Roasting and Frying
During roasting, carbohydrates and proteins are modified as a consequence of the heat treatment, including the caramelization of polysaccharides on the surface of the pulse. In addition, some acids are partially decomposed during roasting, while volatile acids are partially lost due to evaporation. An increase in volume during roasting at the same time the density and kernel weight decrease should be expected. The flavor can also change, especially as a result of the heating processes. Flavor profile of fried peas is great affected by types of oil used for frying. The original raw chickpea is dense and contains no air spaces. But during roasting, the water inside the pulse changes from liquid to vapor, which, given the compact structure of chickpeas, can cause an increase in the vapor pressure of water so that the steam that is generated triggers expansion during roasting. This can lead to development of a large number of air spaces in the cotyledons and give roasted pulse a porous structure and an opaque, chalky appearance.