The review published in the Journal of Food Science & Technology concluded that there is a great deal of potential in the hot extrusion process (above 70⁰C) to enhance nutritional profiles of RTE snacks.
It said that given the projected growth in the snacks segment and increasing demands on health, this proves promising to manufacturers.
“There exists a potential to manipulate the nutritional status of extruded RTEs by altering the digestion potentials of starch and protein, and by the incorporation of bioactive components such as dietary fiber,” the authors wrote.
Highly digestible starch and protein products can be achieved to target consumers doing sport, and relatively low GI and high bioactive containing snacks can be produced for consumers interested in maintaining balanced nutrition, the review said.
Improved digestibility
One of the more widely researched aspects of extrusion impacts on nutrition is the effect on carbohydrate digestibility, the review said.
“The digestibility of starch may be improved by the extrusion process due to partial gelatinisation and fragmentation of starch attributed to the mechanical shearing effect of the extruder on starch granules.”
“Extrusion may be used as a method to initiate the pre digestion of starch; consequently, it is not surprising therefore that extruded snack products tend to be regarded as having high GI status.”
Similarly research has shown that that extrusion technology in RTE snacks can increase the digestibility of protein. Research has indicated that the protein structure is altered from shear conditions during extrusion.
GI shifts
The ability to modify the molecular structure and therefore functionality of starch in extrusion processing can impact glycemic index (GI) levels, it continued.
Research shows that extrusion can up the GI level in snacks: “The depolymerisation of the starch, combined with the high temperatures associated with extrusion, contributes to the fact that starch will be made more readily available to amylolytic enzymes during digestion, and hence extruded snack products tend to yield a higher glycaemic response compared with their unprocessed raw ingredients.”
However, the review also noted that GI levels can be lowered by forming indigestible linkages (complexes) in the snack structure.
This is obviously useful for manufacturers looking to derive products with known digestibility properties but also in producing novel structures and textures, which will appeal to sensory expectations of the modern consumer, the review said.
Enhanced nutrition
The review cites a host of previous research on enhancing the nutritional profile of extruded snacks – including dietary fiber (wheat bran) inclusion.
Research cited suggests that the extrusion process can increase the amount of soluble dietary fiber due to the process altering the molecular structure of components.
Use of pre-germinated grains (mainly rice) has also been studied to enhance the nutritional profile of extruded snacks. In many cases end products contain higher levels of sugar, amino acids and potentially antioxidants.
The role of temperature and shear during extrusion on antioxidant properties has been the topic of much research, the review said, with some concluding that levels are increased when pre-germinated cereals are used.
Pumpkin waste (seeds and skin) has been used to up the fiber and protein content of snacks while regulating blood glucose. Similarly lycopene-rich fiber content from tomato peel and production waste has been used to increase nutrition and bioactive content.
“During the next 10 years, we will undoubtedly see a preponderance of research investigating the effects of extrusion technology on the chemical and nutritional profile of RTE, which will help both the consumer and the food industry to benefit from current research investigating the food structure and nutrition interface,” the review concluded.
Source: Journal of Food Science & Tchnology
Published online ahead of print, doi: 10.1111/ijfs.12055
"Ready-to-eat snack products: the role of extrusion technology in developing consumer acceptable and nutritious snacks"
Authors:M.A Brennan, E. Derbyshire, B.K Tiwari and C.S Brennan