Third generation extruded snacks with ancient grains : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Auckland, New Zealand
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Date
2015
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Massey University
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Abstract
Third generation (3G) is a term that refers to the levels of processing used to produce a finished product.
A 3G snack product starts with a starch based recipe that is extrusion cooked, formed into a dense
shaped pellet and then dried. At this point, it is referred to as semi or half product because it needs to
be further puffed to develop its texture and flavour. The objective of this project was to develop an
unflavoured cereal-based 3G snack formulation with ancient grains. The snack must be unique in shape
and suitable for hot air-puffing.
Two 3G wholegrain base formulations were developed. One formulation was made from coarse rice
flour, wholemeal wheat flour, potato starch, ancient grain blend (one third amaranth, one third quinoa
and one third millet), wheat fibre 600 and salt. The second formulation was maize based by replacing
coarse rice flour with maize polenta. These two base formulations contained ancient grains and
nutrients that provide health benefits and were suitable for air-puffing. A lab-scale model Clextral BC21
twin screw co-rotating extruder was used for this study. Pasting properties of samples were evaluated
using the Rapid Visco Analyser. It was found that ingredient selection and extrusion processing affected
extruded pellets’ paste viscosities, the die swell and product expansion.
Pasting properties of raw ingredient blend were affected by amylose and lipid content, and particle size
of the cereal flour. The more even the raw material particle size was, the more even was the hydration
of the material in the extruder. The results showed that inclusion of dietary fibre (wheat fibre 600, Beneo
GR or Hi-MaizeTM 1043) in the 3G formulations decreased raw ingredients’ and extruded pellets’ paste
viscosities, which resulted in reduced pellet expansion. It was found that wheat fibre 600 at 4 % was
the best fibre choice to produce a 3G snack, because it accelerated extruded pellet drying, helped in
‘pellet checking’ control and producing more uniform cell sized expanded products. Hi-MaizeTM
ingredients were found to lead to the deterioration of viscosity and snack pellet expansion, and therefore
not recommended to be used for 3G snack base formulation.
Increasing the water injection rate to the extruder (from 1.0 to 1.7 L/h) decreased the extruder apparent
torque, thrust pressure, die pressure and SME. The degree of starch degradation was also reduced,
but the product expansion was increased. Pellet expansion was found closely correlated to the pasting
properties of the raw ingredient blend. Pellet expansion increased with the increase of peak viscosity
(PV) and final viscosity (FV) of the raw ingredient blend.
A suitable laboratory drying method was developed for 3G snacks. It was found that drying and holding
at 1 h ± 5 min intervals including a pre-drying step had minimal pellets defects. Humidity control (60 %)
was required throughout this drying process. After puffing, the product sectional expansion index (SEI)
increased with the increase in salt concentration from 0.5 % to 1.0 % and increase in moisture content
from 9.5 % to 12.1 %. The extruded pellets moisture was found to have the most significant effect on
the finished product expansion, and maximum expansion due to puffing was found at 10.6 % pellet
moisture.
A shear-compression analysis of the 3G product prototypes and competitor products showed that most
of low moisture commercial snack products available in the market have low bulk density and were
brittle. The products produced from the proposed 3G formulations were much harder than the
commercial products.
Qualitative consumer focus group studies were conducted to gain insights into consumers’ attitudes
towards extruded snacks, desirable texture and product claims to be included in the product. The results
showed that five themes typically associated with snack consumption (nostalgia, special social
occasions, distraction, convenient treat and hunger). Taste and price were the most important to the
participants, and the health benefits were only an extra bonus. Participants were not tempted by an
ancient grain claim. Product prototypes did not receive very positive feedback due to the taste and the
product size. Product texture was found acceptable by most participants.
This study produced initial formulations for a 3G snack, provided a good starting point for understanding
of the 3G extruded snack process and provided valuable information for further development work.
Further work is required to scale up the recipe, to increase the snack size, to further improve of the 3G
snack flavour without significantly increasing the salt content and to carry out a consumer acceptance
study on the scaled up 3G snack products.
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Keywords
Grain, Ancient grains, Snack foods