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    Development of expanded snack foods containing pumpkin flour and corn grits using extrusion technology : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Md Nor, Norfezah
    The production of expanded snack foods using vegetable powder as an ingredient in ready-to-eat food is rare. In view of its natural desirable colour, flavour, sweetness and health benefits, pumpkin was chosen as an additive to the traditional corn grits or rice used as the basis of an extrusion expanded snack or breakfast food concept. Pumpkins also have a large range of uses as a potentially valuable food for humans and animals. However, they are an underutilised product. This study was undertaken to demonstrate the potential of pumpkin products as additives in expanded snack food products. Processing the fresh pumpkin into flour dramatically extends the shelf life and makes the ingredient available throughout the year. The flour is more convenient for extrusion as it is stored and handled as a dry powder. Research was conducted to produce and characterise pumpkin flour made by convection oven and freeze drying of a pumpkin fractions such as peel, pulp (rind), flesh and seed. The flour was combined with corn grits in various proportions up to a maximum of 20% w/w. After determining suitable processing conditions and the maximum acceptable concentration of pumpkin flour for an edible product, the effect of process parameters on product quality were determined. Finally the product was optimised using response surface methodology (RSM). The proximate compositions of pumpkin flour from convection oven and freeze drying were as expected identical to commercial pumpkin flour. The carbohydrate content ranged between 69.8 and 89%, protein ranged between 1.3 and 21%, and fat between 0.03 - 0.53%. Pumpkin flour produced by freeze drying revealed L, a and b values higher than in commercial pumpkin flour, indicating that the flour was lighter in colour and appeared more orange than that oven dried. The effect of varying pumpkin flour proportion at two mass flow rates of 7.5kg/hr and 8.5kg/hr revealed that mass flow rate did not have any significant correlation to the extrusion parameters and the final quality of the expanded snack product. However, a high quality final product can be achieved at all mass flow rates with less than 20% pumpkin flour incorporated into the blend. Varying the proportion of pumpkin flour between 5% and 20% in combination with corn grits using screw speeds of 250rpm and 350rpm showed that, increasing the proportion of pumpkin flour to 20% significantly (P<0.05) decreased specific mechanical energy (SME) and torque. The extruded pellets using a 20% blend of pumpkin with corn grits were harder, more denser and less expanded than those made with higher proportions of corn grits. The crispiness and hardness of the final product was not closely related to the number or area of bubbles present in the structure. Screw speed did not significantly (P>0.05) affect the specific mechanical energy (SME) or the physical characteristics of the final product. Hardness seemed to be due to bubble wall stiffness i.e. effectively the thickness and rigidity of the set starchy matrix. Response surface methodology (RSM) was predicted four solutions for optimum conditions which can be achieved at barrel temperature ranging from 165°C to 167°C at a constant feed rate of 10.50kg/hr and pumpkin flour percentage ranged from 16% to 17%. With these conditions, the optimum SME of 0.15 was achieved and this product had a maximum radial expansion of 11.00%, hardness less than 142.0N with a total carotenoid content of 2.07ppm to 2.13ppm. Sensory analysis revealed most consumers preferred expanded snack products containing 5% pumpkin flour and produced by extruding at a barrel temperature of 170°C and mass flow rate of 12.0kg/hr. The panellists indicated that they would buy this product due to its acceptable taste, texture, odour and overall product characteristics. However, the expanded snack with 15% pumpkin flour was found to have highest total carotenoid content (5.78ppm) and protein content (28.8%) after processing and may have been, in nutritional terms, the best product. The slowly digestible starch (SDS) value and carbohydrate content of this product was found at 97.03mg/g and 59.29% respectively. From this work useful information regarding pumpkin flour and its application in extruded expanded snack production was obtained. This work has the potential to diversify the application of pumpkin flour and offer new uses for pumpkin in the food industry.
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    Comparison of heritage and modern crop cultivars in response to irrigation and nitrogen management : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2012) Fandika, Isaac Rhinnexious
    There is a resurgence of interest in heritage crop cultivars (potatoes, squash and yams) in New Zealand because of the premiums farmers get at niche markets. However, a paucity of information in relation to their growth characteristics and resource use efficiency limit successful management of these crops. This research compares the response of different heritage and modern crop cultivars to irrigation, nitrogen (N) fertiliser and canopy management. Some heritage cultivars produced as much marketable yield as modern cultivars while other heritage cultivars had low yields. Modern potatoes were more responsive to irrigation and N than heritage potato crops (collectively known as Taewa). Application of more than 80 kg N ha-1 decreased yield in Taewa (Moe Moe, Tutaekuri) whereas, it increased the yield of modern potatoes (Agria, Moonlight). Full irrigation (FI) increased yield in modern potatoes and Moe Moe. In contrast, Tutaekuri yield was greatest with partial irrigation (PI). FI and 80 kg N ha-1 are recommended for Moe Moe production whereas PI and less than 80 kg N ha-1 are recommended for Tutaekuri. In addition, greater tuber dry matter and low sugar content suggest that Taewa would have better cooking and processing qualities than modern potatoes. Heritage crops required more water than modern crop cultivars because they mature later. There was high ‘water use efficiency’ in heritage pumpkin squash; high ‘irrigation water use efficiency’ in modern potatoes and high ‘economic water productivity’ for heritage potatoes and pumpkin squash. Heritage crop cultivars adapted to water deficit by developing more roots, higher photosynthetic WUE and leaf water potential than modern cultivars. Although total biomass production was similar, heritage crops tended to produce less marketable yield than modern cultivars because of excessive vegetative growth and potato psyllid infestation. Two strategies to manage the canopy and reduce vegetative growth using chlorocholine chloride (CCC) and mechanical topping were developed. Both strategies increased marketable yield in Taewa by 32 - 44%. Application of CCC at 25 and 50 days after emergence (DAE) was recommended for irrigated Taewa, whereas mechanical topping and application of CCC at 25 and 30 DAE were recommended for both irrigated and rain-fed Taewa. The study also observed that potato psyllid need to be controlled up to 170 DAE in Taewa to avoid yield loss equivalent to NZ$10, 485 to NZ$17, 412 per ha. This study contributes to policy on sustainable and improved Maori land use. It can be concluded that premium market prices are important to the success of heritage crops (i.e. to maintain their high ‘economic water productivity’) whereas modern crops might use irrigation water more efficiently (i.e. greater ‘water use efficiency’). It is evident that heritage crops can be grown successfully, and that on occasions they use valuable resources efficiently. To enhance water use efficiency, management of heritage crops should focus on improving the harvest index.