Degree of biomass substrate solubilization

When evaluating the effect of pretreatment and especially enzymatic hydrolysis of biomass, we normally measure the monomeric sugar produced. At most time, quite a lot of soluble oligomers existing in the hydrolyzates that could not be measured by the standard HPLC analysis, which will lead to lower hydrolysis yield. This can be confirmed by post-dilute acid hydrolysis, showing several fold increase in  monomeric sugars (glucose and xylose) yield. The reason for this is that most of the commercial enzyme cocktails are not for global use and need customization for a specific biomass substrate. Some new technology ends up with strains than can work on low DP soluble sugars. Therefore, measurement of the degree of biomass solubilization after pretreatment or/and enzymatic hydrolysis will be useful information for the estimation of the treatments.  A weight loss is rough, but quick method.

Universal or “customized” enzyme cocktail for sugar production

Currently available commercial enzyme preparations are limited in number and composition and have generally been optimized for acid-pretreated stover from maize and other grasses.

However, lignocellulosic feedstocks for sugar production include a variety of biomass: woody biomass such as softwood and hardwood, waste paper; non-wood biomass such as grass stovers (e.g., maize, sorghum, switchgrass or Miscanthus); and other biomass materials such as corn cobs, dried distillers’ grains solubles. All these biomass have different chemical composition, which will response differently to different pretreatments (e. acidic, basic, or oxidation), resulting in pretreated biomass with different chemical composition, even sugar composition. Therefore a general enzyme cocktail may work well for one type biomass or one type of pretreated biomass but not efficiently for other biomass. For example, for grass biomass with branchy arabinose and glucuronic acid, it may need GH10 endo-xylanase, a-arabinosidase, and a-glucuronidase. For woody biomass, in addition to the key endo-and exo-glucanases and endo-xylananse, it may need ferulate esterase and beta-mannanase. For acid pretreatment at a temperature >160 C, some of biomass hemicelluloses will be removed but some lignin may condense or re-deposit on fiber surface; while alkaline pretreatment will delignify but may have hemicelluloses re-deposited on the fiber surface. All of these will impact the efficiency of enzymatic hydrolysis and may require specifically modified enzyme cocktails. Therefore, a modified “customized” enzyme cocktail is more appropriate to adapt the spectrum of biomass and pretreatment combination for target hydrolysis.

A good research paper presents a study on this issue.

Partial recycling of pre- treated biomass will increase C6 sugar recovery yield

The chemical kinetics of the sulfuric acid hydrolysis

The chemical kinetics of the sulfuric acid hydrolysis of softwood was determined by J.F.Seaman in 1945 as follows:

• a 100% increase in acid concentration causes an increase of 153% in the k1 cellulose-hydrolysis-rate kinetics constant, but that increase only caused the k2-sugar product-degradation kinetics constant to increase 103%.
• a 10 degree rise in C temperature causes an increase of approximately 190% in the k1- cellulose-hydrolysis-rate kinetics constant, but then k2-sugar-product-degredation kinetics constant increased only 130%.