Production of short-chain fatty acids and gas from various oligosaccharides by gut microbes of carp (Cyprinus carpio L.) in micro-scale batch culture.

We studied the metabolism of various oligosaccharides by carp (Cyprinus carpio) hindgut microbes by measuring gas productivity and organic acid production in gut contents using a 50-microl-scale batch culture system. Carp hindgut contents were incubated with 500 microg each of raffinose, lactosucrose, kestose, lactulose, gentiobiose, 4'-galactosyllactose and 6'-galactosyllactose and soybean-, xylo-, and isomalto-oligosaccharides or none (blank culture) at 25 degrees C for 6 h. The time-course of gas release from the culture (Y microl/culture) was expressed as an exponential function of incubation time (t) [Y=A+Bx(1-e(-kt))]; A, B and k are constants). Potential production of gas (A+B) from soybean-oligosaccharide and raffinose was larger than for the other saccharides except for kestose, and blank culture. The rate constant of gas (k) for lactosucrose was larger than that for isomalto- and xylo-oligosaccharide, lactulose, kestose or blank culture. Net production of total SCFA (sum of acetic, propionic and n-butyric acid weights) from cultures with soybean- and isomalto-oligosaccharides, raffinose, gentiobiose and lactosucrose was greater than that from blank culture. These results suggested that soybean-oligosaccharide and raffinose were potentially highly fermentable oligosaccharides for carp hindgut microbes. Chemical structures of oligosaccharides seem to play an important role in the fermentability. It is also likely that oligosaccharide utilization differs between mammals and teleosts.