Osmotic Pressure Potential Research Articles

Delactosed Whey Permeate as Substrate for Succinic Acid Fermentation by Actinobacillus succinogenes

Delactosed whey permeate (DLP) is the remnant after the concentration of deproteinized whey permeate and separation of the lactose. As the milk industry expands, the surplus of the waste product DLP increases. This work evaluates DLP for succinic acid production in batch cultures with mildly halotolerant Actinobacillus succinogenes 130Z. The elemental composition of delactosed whey permeate is analysed, adjusted by supplementing with peptone and NaHCO3, and used in submerged fermentations. The obtained succinic acid yield with DLP based media is ranged between 0.62 and 0.67 gSA/gLactose, with minimal by-products. Growth (Kx) and non-growth (mATP) associated maintenance energies of A. succinogenes were estimated via ATP balance using batch fermentation data on both DLP media as well as conventional simulated media (TSB). For mATP, the estimated value is 7.4 mmol/gDCW/h for DLP media, which is compatible with commercial TSB media. Herein, we clearly demonstrate use of delactosed whey permeate as a promising substrate for succinic acid fermentation, despite high ionic strength and osmotic pressure potential.

Effects of Dehydration on the Viscoelastic Properties of Vocal Folds in Large Deformations

Dehydration may alter vocal fold viscoelastic properties, thereby hampering phonation. The effects of water loss induced by an osmotic pressure potential on vocal fold tissue viscoelastic properties were investigated. Porcine vocal folds were dehydrated by immersion in a hypertonic solution, and quasi-static and low-frequency dynamic traction tests were performed for elongations of up to 50%. Digital image correlation was used to determine local strains from surface deformations. The elastic modulus and the loss factor were then determined for normal and dehydrated tissues. An eight-chain hyperelastic model was used to describe the observed nonlinear stress-stretch behavior. Contrary to the expectations, the mass history indicated that the tissue absorbed water during cyclic extension when submerged in a hypertonic solution. During loading history, the elastic modulus was increased for dehydrated tissues as a function of strain. The response of dehydrated tissues was much less affected when the load was released. This observation suggests that hydration should be considered in micromechanical models of the vocal folds. The internal hysteresis, which is often linked to phonation effort, increased significantly with water loss. The effects of dehydration on the viscoelastic properties of vocal fold tissue were quantified in a systematic way. A better understanding of the role of hydration on the mechanical properties of vocal fold tissue may help to establish objective dehydration and phonotrauma criteria.