Semi-solid extrusion-based 3D printing of biopolymer hydrogels and their applications in food

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2021-08
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Kuo, Chih-Chun
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Shi, Xiaolei
Clark, Stephanie
Acevedo, Nuria
Mellata, Melha
Qin, Hantang
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Food Science and Human Nutrition
Abstract
Probiotics are increasingly incorporated into food products to convey their health benefits. According to previous studies, the efficacy of probiotics are strongly related to bacteria strain, dosage, and viability; however, there are three major challenges of the current probiotics market: 1) the current production approach is not designed to customize the dosage and strains to fulfill the need of each individual; 2) probiotic-containing products on the market are mostly dairy-based, and non-shelf-stable; 3) it is also challenging to maintain the viability of probiotics strains throughout production and during storage. To overcome these challenges, we proposed to manufacture a novel delivery system for probiotics using integrated processes of encapsulation, 3D printing, and freeze-drying. The overall goal of this study was to investigate the feasibility of fabricating edible 3D printed biopolymer-based hydrogels as carriers for live probiotics. The objectives of this study were to 1) determine the optimal formulations of gelatin-alginate (G/A) hydrogels based on their 3D printability during the encapsulation and 3D printing processes, and the mechanical properties and overall product quality after the integrated process; 2) evaluate the viability of Bifidobacterium lactis and Lactobacillus acidophilus within the three optimal formulations after the integrated manufacturing processes; 3) assess the physico-chemical properties and shelf life of the final products. In these studies, the optimized G/A hydrogels (3% G/A 2:1, 5% G/A 1:1, 7% G/A 1:2) were used to upload two selected strains, i.e., Bifidobacterium lactis and Lactobacillus acidophilus at levels of approximately 1010 and 109 CFU/g, respectively. The probiotic-containing hydrogels were then loaded into a sterile syringe for the 3D printing process. After the 3D printing process, post-processing of freeze-drying (24 hr, frozen at -18°C for 2 hours prior to freeze-drying) was conducted to dehydrate the hydrogels. The results showed that the optimal G/A hydrogels demonstrated a shear-thinning behavior and viscoelasticity of storage modulus (Gʹ) higher than loss modulus (Gʺ), with a loss factor (tan δ= Gʺ/Gʹ) in the range of 0.48-0.61 at the frequency sweep of 15-40 rad/s. Viable cell counts of Bifidobacterium lactis and Lactobacillus acidophilus were able to be maintained at a level larger than 9 log CFU/g and 6 log CFU/g, respectively, after the integrated process of encapsulation, 3D printing, and freeze-drying. This work shows the potential of fabricating a shelf-stable and convenient product or supplement to carry customized strains and dosage of live probiotics.
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