Drying Kinetics and Expansion of Non‐predried Extruded Starch‐Based Pellets during Microwave Vacuum Processing

Self Cite

The influence of the degree of gelatinization (DG) on microwave‐induced expansion of starch‐based, extruded pellets under vacuum was investigated. Expansion of extruded pellets with initial DG between 43.6 and 72.9% was investigated in a microwave vacuum drying system. With increasing DG, volume expansion showed a linear increase. The number of pores significantly increased at DG above 64.2%. A larger amount of water available might be the reason for the increased nucleation at large DG. The pore sizes decrease with increasing number of pores. If a larger number of bubbles is nucleated, a fewer amount of water can diffuse into every single bubble possibly resulting in lower water vapor pressure. No relationship between rheological and expansion properties of the matrix could be observed. We therefore assume that nucleation has the strongest effect on pore size distribution. Practical Applications In contrast to direct‐expanded extruded snacks, third‐generation snacks are generally produced by predrying nonexpanded, extruded pellets, followed by expansion to achieve a crispy and porous texture. By this procedure, extrusion can be performed at high moisture contents, moderate temperatures and moderate shearing conditions. This way, thermal‐ and mechanical‐sensitive ingredients can be preserved. A distinctive feature of the process investigated in this study is that the expansion is achieved by microwave vacuum processing, which allows an indirect expansion without the time‐ and energy‐consuming predrying process. This study shows that total volume and inner structure of the expanded pellets is influenced by the degree of gelatinization. With these information, producers can turn structure‐related properties such as appearance, crispiness and crunchiness to targeted values.

Section: Extrusionmentioning

confidence: 99%

Influence of Degree of Gelatinization on Expansion of Extruded, Starch‐Based Pellets during Microwave Vacuum Processing

Kraus

Enke

Gaukel

et al. 2014

Self Cite

“…A detailed description of the extrusion process and the sample handling can be found in Kraus et al . ().…”

Section: Methodsmentioning

confidence: 97%

Influence of Sucrose Content on Expansion of Extruded, Starch‐Based Pellets during Microwave Vacuum Processing

Kraus

Enke

Schuchmann

et al. 2014

Self Cite

The influence of sucrose content on microwave‐induced expansion of starch‐based, extruded pellets under vacuum was investigated. Expansion of extruded pellets with different sucrose contents (0, 10 and 20%) was investigated in a microwave vacuum‐drying system. With increasing sucrose content, volume expansion showed a nearly linear increase. Also, the number of pores increased with increasing sucrose content. A softening of the matrix might facilitate nucleation. Pore areas decrease with increasing number of pores. We therefore assume that nucleation has the strongest impact on pore area distribution. Mainly pillow‐shaped and round final products were found. The shape of the final products could be related to the glass transition temperature Tg of the intermediate products and to heating and drying characteristics of the pellets during microwave vacuum processing. Tg decreases with increasing sucrose contents. If expansion of the initially cylindrical pellets takes place within the rubbery state, round final products are formed. If a glassy outer layer is built due to evaporation cooling of the surface and high Tg of the matrix, the pellets rupture upon expansion and the pillow shape forms. Practical Applications In contrast to direct expanded extruded snacks, third‐generation snacks are generally produced by pre‐drying nonexpanded, extruded pellets, followed by a separated expansion process. By this process route, extrusion can be performed at high moisture contents, moderate temperatures and moderate shearing conditions. This is beneficial in terms of preserving thermal‐ and mechanical‐sensitive ingredients. A special feature of the process investigated in this study is that the expansion is achieved by microwave vacuum processing that allows an indirect expansion without a time‐ and energy‐consuming pre‐drying process. This study shows that total volume and inner structure of the expanded pellets is strongly influenced by the amount of sucrose added to the starch‐based matrix. With these information producers can turn structure‐related properties such as appearance, crispiness and crunchiness to target values.

“…; Kraus et al . ):

OP = \frac{Particle density - bulk density}{Particle density} \times 100

CP = \frac{Material density - particle density}{Material density} \times 100

TP = \frac{Material density - bulk density}{Material density} \times 100

…”

Section: Methodsmentioning

confidence: 99%

Optimization of Leavening Agents in Extruded Gluten‐Free Brewer's Rice Hard Pretzel Using Response Surface Methodology

Paykary

Karim

Saari

et al. 2015

Celiac is the second most important issue in food sensitivities. The only treatment for celiac is a lifetime avoidance of consuming gluten. As pretzels are one of the most popular snacks in the world, making gluten-free pretzels is a market need. To produce gluten-free products, it is important to optimize the ingredients of the formulation. This research focused on optimization of the leavening agents of the most popular commercial hard pretzel formulation in which wheat flour is replaced with brewer's rice flour. This research also attempts to explain the effect of leavening agents in products containing no matrix molecules such as gluten. Response surface methodology via the central composite design was used to optimize the effects of yeast and bicarbonate of soda on the hardness (cutting strength), fracturability (brittleness), surface color, lateral expansion, expansion ratio, specific length, density (bulk, particle, material), porosity (open, close, total), water absorption index, water solubility index, water holding capacity, oil absorption index and oil holding capacity of gluten-free hard pretzel. The optimized results indicated that the gluten-free pretzel requires 8.05g yeast and 2.59g bicarbonate of soda for every 500g of brewer's rice flour. PRACTICAL APPLICATIONSThe study investigated the effect of leavening agents (yeast and sodium bicarbonate) which are critical ingredients affecting the quality characteristics, consumer preference and palatability of gluten-free hard pretzel when typical soft wheat flour was replaced with a gluten-free flour like rice or brewer's rice flour. The result guides the gluten-free industries on the importance of using the suitable amount of leavening agents for production of acceptable physicochemical and textural properties of not only hard pretzel, but also for other low moisture cereal products as well. The findings also introduce the usage of brewer's rice, a by-product of rice milling industry as one of the ingredients for the production of value-added products for all consumers' especially the celiac sufferers who need to find more reasonable price products compared to gluten ones.