Lactic Acid and Thermal Treatments Trigger the Hydrolysis of Myo-Inositol Hexakisphosphate and Modify the Abundance of Lower Myo-Inositol Phosphates in Barley (Hordeum vulgare L.)

Abstract

Barley is an important source of dietary minerals, but it also contains myo-inositol hexakisphosphate (InsP6) that lowers their absorption. This study evaluated the effects of increasing concentrations (0.5, 1, and 5%, vol/vol) of lactic acid (LA), without or with an additional thermal treatment at 55°C (LA-H), on InsP6 hydrolysis, formation of lower phosphorylated myo-inositol phosphates, and changes in chemical composition of barley grain. Increasing LA concentrations and thermal treatment linearly reduced (P<0.001) InsP6-phosphate (InsP6-P) by 0.5 to 1 g compared to the native barley. In particular, treating barley with 5% LA-H was the most efficient treatment to reduce the concentrations of InsP6-P, and stimulate the formation of lower phosphorylated myo-inositol phosphates such as myo-inositol tetraphosphate (InsP4) and myo-inositol pentaphosphates (InsP5). Also, LA and thermal treatment changed the abundance of InsP4 and InsP5 isomers with Ins(1,2,5,6)P4 and Ins(1,2,3,4,5)P5 as the dominating isomers with 5% LA, 1% LA-H and 5% LA-H treatment of barley, resembling to profiles found when microbial 6-phytase is applied. Treating barley with LA at room temperature (22°C) increased the concentration of resistant starch and dietary fiber but lowered those of total starch and crude ash. Interestingly, total phosphorus (P) was only reduced (P<0.05) in barley treated with LA-H but not after processing of barley with LA at room temperature. In conclusion, LA and LA-H treatment may be effective processing techniques to reduce InsP6 in cereals used in animal feeding with the highest degradation of InsP6 at 5% LA-H. Further in vivo studies are warranted to determine the actual intestinal P availability and to assess the impact of changes in nutrient composition of LA treated barley on animal performance.

Treatment of grain with organic acids at 2 different dietary phosphorus levels modulates ruminal microbial community structure and fermentation patterns in vitro

“…These results also indicate that if P requirements of the rumen microbes are not met through readily available inorganic sources (diet or P recycled in saliva), rumen microbes may upregulate their endogenous phytase expression with CAc processing of barley. Another plausible reason may be that barley processing with CAc released P from InsP 6 as recently shown for LAc-treated barley (Metzler-Zebeli et al, 2014). Because nearly 61% of barley P (Metzler- Zebeli et al, 2014) and 50% of soybean meal P (Viveros et al, 2000), which were the major P sources in our basal diet, is InsP 6 , we assume that almost 2 g from the total 3.1 g of P/kg of DM of the native diet was InsP 6.…”

“…We recently showed that treating barley grain with organic acids modified the nutrient composition and enhanced the hydrolysis of InsP 6 Metzler-Zebeli et al, 2014;Harder et al, 2015a). This study aimed to evaluate the effects of barley grain treated with CAc and LAc on the abundance of welldescribed ruminal microbial populations, their microbial fermentation patterns, and nutrient degradation in vitro.…”

“…This finding has important practical implications, particularly with respect to treatment effects of barley with CAc and LAc, which may have alleviated the lack of available P by stimulating both overall microbial abundance and their metabolic activity to utilize dietary P sources and produce SCFA. The reason for this might again be the improvement of degradation of InsP 6 by acidic treatment of grains (Haraldsson et al, 2004;Metzler-Zebeli et al, 2014) and thus the increase in ruminal availability of P for ruminal bacteria. We also assume that the acid treatment might have improved the accessibility for ruminal microbes to the aleurone layer of barley and thereby to the storage location of InsP 6 (Reddy et al, 1982).…”

“…The soaking procedure was the same as used in our previous work (Harder et al, 2015a,b). We used concentrations of 50.25 g/L CAc and 76.25 g/L LAc because these concentrations showed the best results both in terms of InsP 6 hydrolysis (Metzler-Zebeli et al, 2014) and modification of other chemical components of barley (Harder et al, 2015a,b). On average, each gram of barley grain absorbed 0.75 mL of fluid.…”

“…Haraldsson et al (2004) showed that treating cereals with low concentrations of lactic acid (LAc), a mild organic acid widely used in food technology, promoted the hydrolysis of InsP 6 . More recently, Metzler-Zebeli et al (2014) reported a linear increase in the hydrolysis of InsP 6 by treating grain with graded levels of LAc from 7.63 to 76.25 g/L LAc. In addition, we have observed that processing grain with 76.25 g/L LAc results in an increase of slowly digestible starch (Deckardt et al, , 2015.…”