María A. García

Film forming capacity of chemically modified corn starches.

Native starch can be chemically modified to improve its functionality and to expand its uses. Modified starches were characterized and the rheological behavior of filmogenic suspensions was analyzed. The film forming capacity of different chemical modified corn starches was evaluated. Acetylated starch was selected by the characteristics of the resulted films; its optimum concentration was 5% w/w since their films exhibited the lowest water vapor permeability (WVP, 1.26×10(-10)g/msPa). The effect of glycerol as plasticizer on film properties depend on its concentration, being 1.5% w/w those that allows to obtain the lowest WVP value (1.64×10(-11)g/msPa), low film solubility in water and a more compact structure than those of unplasticized films. Mechanical behavior of plasticized acetylated starch films depends on glycerol concentration, being rigid and brittle the unplasticized ones, ductile those containing 1.5% w/w of glycerol and very flexible those with a higher plasticizer content.

Characterization of Starch and Composite Edible Films and Coatings

Starch-based and composite edible films and coatings can enhance food quality, safety and stability. They can control mass transfer between components within a product, as well as between product and environment. They can improve performance of the product through the addition of antioxidants, antimicrobial agents, and other food additives. Unique advantages of edible films and coatings can lead to the development of new products, such as individual packaging for particular foods, carriers for various food additives, and nutrient supplements. Film materials and their properties have been reviewed extensively in this book and previously (Guilbert 1986; Kester and Fennema 1986; Krochta and De Mulder-Johnson 1997).

Enhancement of thermoplastic starch final properties by blending with poly(ɛ-caprolactone).

Final properties of two thermoplastic corn starch matrices were improved by adding poly(ɛ-caprolactone), PCL, at 2.5, 5, and 10% w/w. One of the thermoplastic starch matrices was processed using water and glycerol as plasticizers (SG) and the other one was plasticized with a mixture of glycerol and sodium alginate (SGA). Blends were suitably processed by melt mixing and further injected. Films obtained by thermo-compression were flexible and easy to handle. Microstructure studies (SEM and FTIR) revealed a nice distribution of PCL within both matrices and also a good starch-PCL compatibility, attributed to the lower polyester concentration. The crystalline character of PCL was the responsible of the increment in the degree of crystallinity of starch matrices, determined by XRD. Moreover, it was demonstrated by TGA that PCL incorporation did not affect the thermal stability of these starch-based materials. In addition, a shift of Tg values of both glycerol and starch-rich phases to lower values was determined by DSC and DMA tests, attributed to the PCL plasticizing action. Besides, PCL blocking effect to visible and UV radiations was evident by the incremented opacity and the UV-barrier capacity of the starch films. Finally, water vapor permeability and water solubility values were reduced by PCL incorporation.

Agro-industrial residue from starch extraction of Pachyrhizus ahipa as filler of thermoplastic corn starch films.

Biocomposites films based on thermoplastic corn starch (TPS) containing 0.5% w/w fibrous residue from Pachyrhizus ahipa starch extraction (PASR) were obtained by melt-mixing and compression molding. PASR is mainly constituted by remaining cell walls and natural fibers, revealed by Scanning Electron Microscopy (SEM). Chemical composition of the residue indicated that fiber and starch were the principal components. Biocomposites thermo-stability was determined by Thermo-Gravimetric Analysis. A continuous PASR-TPS interface was observed by SEM, as a result of a good adhesion of the fibrous residue to starch matrix. Likewise, films containing PASR presented fewer superficial cracks than TPS ones, whereas their fracture surfaces were more irregular. Besides, the presence of PASR increased starch films roughness, due to fibers agglomerates. Films reinforced with PASR showed significantly lower water vapor permeability (WVP). In addition, PARS filler increased maximum tensile strength and Youngs modulus of TPS films, thus leading to more resistant starch matrixes.

Fermentation and drying effects on bread-making potential of sour cassava and ahipa starches

Cassava sour starch is a gluten-free product obtained by natural fermentation and sun-drying that outstrips the native starch baking expansion properties. Although maize starch has been subjected to a similar process, this desirable feature could not be achieved. Ahipa, an unexploited tuberous root, renders starch with relatively low gelatinization temperature and amylose content, like that of cassava. The aim of this work was to study the characteristics and technological properties of ahipa starch subjected to different fermentation processes and drying methods (oven- or sun-drying) and compare the bakery quality of its derived products to those from fermented cassava starches. Ahipa starch followed similar fermentation paths to those followed by cassavas, and sun-drying significantly reduced the content of the resultant lactic and butyric acids. Rheological behavior of starch pastes as well as moisture content and hardness of the doughs obtained from fermented and sun-dried ahipa starches differed from those of cassava. Sun-light exposure resulted detrimental for the expansion properties of ahipa sour starches, while the native one showed baking expansion properties like those of fermented sun-dried cassava starch. Thus, ahipa starch represents an interesting ingredient for the elaboration of gluten-free baked products.