Typical tropical broiler feed formulations contain high percentages of corn and high proportions of starch as well. Under processing conditions using heat and moisture, starches get gelatinized, which then help in binding other feed particles together, from the ones used in feed formulations. Starch gelatinization is an order-disorder phase change that includes the diffusion of water into a starch granule, hydration and swelling, uptake of heat, loss of crystallinity of starch granule and amylose leaching. Leached amylose immediately forms double helices that may aggregate (hydrogen bond) to each other and create semicrystalline regions. It is speculated that as the gelatinized starch cools, the dispersed matrix forms a gel or pastelike mass that may function as an adhesive or binding agent.
Several research studies have associated dietary gelatinized starch both positively and negatively with pellet quality and broiler performance. However, it has been accepted now that gelatinized starch per se may affect broiler performance, apart from its contribution to pellet binding. Gelatinizing cereal starch has generally been thought to improve enzymatic access to glucosidic linkages and consequent digestibility. A researcher reported a significant improvement in weight gain and feed conversion in chicks fed pelleted and reground corn that was incorporated into a complete diet over chicks fed similar diets with unprocessed corn.
The susceptibility of starch granules to enzyme action is of considerable importance. Digestibility of starch is affected by many factors including the nature and physical form of the starch including amylose and amylopectin ratio. The susceptibility of strach to enzymes can be increased by gelatinization or by any other process that destroys the granular structure of starch. Larger granules of starch gelatinize at a lower temperature and small granules at a higher one. The lower the moisture content, the higher is the temperature required to produce gelatinization.
Another area of interest concerns over the fate of starch that has escaped amylosis in the small intestine and will pass into the large intestine. Poor digestibility of starch in the large intestine may prove detrimental to the birds, by helping proliferation, eg Coliforms, and in combination with pathological challenges this will lead to the characteristic wet litter. Poor digestibility could due to poor processing of raw starch used in the formulation of diets for high producing poultry.
Indian corn is one of the oldest varieties of corn, its kernels, which has “hard as flint” shells has also been given its name as “Flint corn”. Flint corn kernels contain a small amount of soft starch surrounded completely by a larger amount of hard starch, which means the kernels shrink uniformly during drying process and are dent-free and hence less prone to spoiling (adapted for harsh and hot – humid tropical conditions). Despite its tough exterior, this type of corn get infested by mold and mycotoxins which is consumed by livestock and humans, and is a classical example of tropical climatic challenges.
The digestibility of corn cereal is also greatly influenced by the large starch component, especially the ratio between amylose and amylopectin. Amylopectin is more readily digested than amylose due to its amorphous nature. In research on broiler chickens, it is reported that the terminal ileal digestibility of maize starch rarely exceeds 85%. The undigested starch at the terminal ileum is assumed to be “resistant” to digestion and presents an opportunity for use of microbial enzyme supplements in maize-based diets. Amongst the three types of resistant starch found in cereals, two types are known to be caused by inherent factors during the formation of the grain while a third, referred to as RS3 is created by processing and storage conditions. Indian cornalso exceeds over the international corn average in amylose content as well as RS3 factor.
Indian corn also has higher number of corn seeds, average 450 in every 100 gm than the USA grain that has a range of 300-350. This higher number of corn seeds in a given mass gives further challenge to cook these hard kernels and bind them during feed pelleting, in case of inefficient or insufficient starch gelatinization. On one hand these physical features of local corn makes it a tough choice to gelatinize its starch during conditioning and pelleting, while on the other hand, use of short time conditioners by most of the feed millers based on borrowed engineering calculations from western world, and out of sheer ignorance, makes this starch gelatinization all together a more challenging job. These short-term conditioners are neither able to provide enough moisture and heat to cook and gelatinize local corn starch rich feed formulation nor enough moisture transfer from the steam in the mash meal in the conditioner.Currently most of the feed millers are using “short time conditioners” in India that offers only 15-30 seconds of conditioning time.
Tropical climatic and storage conditions of corn and other raw materials make the starch further dried up and retrograded by loosing the inherent bound moisture. This drying and consistent loss of moisture by corn during storage further makes its conditioning difficult in “Short Time Conditioners”.
Harsh tropical climatic conditions, dried up corn starch, tough corn kernels, higher number of corn grains in given mass, wide use of short time conditioners, wrong steam volume and quality going inside the conditioner, addition of surfactants are the factors making adequate starch gelatinization a difficult job for tropical feed millers. Poor starch gelatinization has proven link to poor digestibility of feed, wet litter, more fines in the feed, low pellet durability or softer pellets and low moisture in the final feed.
To produce high-quality pellets , feed millers from South Asian climatic conditions must strategise to gelatinize as much ingredient starch as possible. High-quality pellets are not only desirable but a must now as their feeding is correlated with improved broiler performance. Improving pellet quality through increasing starch gelatinization cannot only help nutritionsits in satisfying the dietary needs of the animal without over formulating it with excess nutrients or feed additives but can also positively affect nutrient utilization, thus enhancing the performance boosts.
To efficiently gelatinize these high degree of crystallized starches of tropical corns and other ingredients, the meal moisture must approach 15-16% moisture in the conditioner and the temperature of mash meal must be set to achieve at least 82.5°C. The further high setting up of conditioning temperature (up to 90-93°C) by the few feed millers are indicative of the high degree of crystallinity in local corn starch because of its dryness and low moisture. High conditioning temperature set helps the feed millers achieve the high transition temperature needed to gelatinize dried up corn, whichis otherwise difficult to gelatinize at lower temperature. The hotter the meal, the greater the degree of gelatinization realized but it also risks the loss of nutrients. To preserve this processing loss of nutrients duringfeed pelleting and conditioning, a proper steam pipeline at normally low-pressure steam must be implemented.