The pH of the assay solution after the sample is added should be the same as that of the assay buffer that is supplied with the kit.
Low sample volumes (e.g. 0.1 mL) are not likely to affect the pH of the assay solution and therefore may not require pH adjustment.
Samples above 0.1 mL are more likely to affect the pH of the assay solution and therefore the pH of these samples should be adjusted as described in the data booklet, prior to addition to the assay.

Sometimes the addition of the last assay component can cause a small negative absorbance change in the blank samples due to a dilution effect and in such cases it is recommended that the real absorbance values be used in the calculation of results.

The kit can be used for any type of galactomannan.  However, to calculate the galactomannan content, you will need to know the galactose/mannose ratio of the galactomannan.

Carob and Guar galactomannan can be measured using essentially the same procedure.

If you suspect that the Megazyme test kit is not performing as expected such that expected results are not obtained please do the following:

1. Ensure that you have tested the standard sample that is supplied with the Megazyme test kit.
2. Send the results of the kit standard, blank samples and the results obtained for your sample, in the relevant MegaCalc spreadsheet (if available) to Megazyme (cs@megazyme.com). Where available the relevant MegaCalc spreadsheet can be downloaded from where the product appears on the Megazyme website.
3. State the kit lot number being used (this is found on the outside of the kit box).
4. State which assay format was used (refer to the relevant page in the kit booklet if necessary).
5. State exact details of any modifications to the standard procedure that is provided by Megazyme.
6. State the sample type and describe the sample preparation steps if applicable.

Yes, we did a lot of work on guar gum from numerous samples, and the value we found for it was 38% +/- 1% galactose. 

The Megazyme Galactomannan Kit measures guar and carob galactomannans.  The method is based on hydrolysis of galactomannan to galactose and manno-oligosaccharides and the galactose is measured with galactose dehydrogenase.  The method could be adapted for levels of 0.3%.

Megazyme product C-NAD25 is suitable.

Sigma product N-7004 is a suitable alternative to Boehringer Mannheim 662046 and can be used at the same volume per test.

Yes, we believe that it is possible to accurately measure the galactomannan content based on the known galactose/mannose ratio.  In studies we performed many years ago, we found that there was little difference in the ratio of galactomannans extracted from a wide range of carob seed varieties or of guar seed varieties; please refer to the papers cited below:
McCleary, B. V. (1981).  Galactomannan quantitation in guar varieties and seed fractions.  Lebensm. – Wiss. Technol., 14, 188-191.
McCleary, B. V., Dea, I. C. M., Clark, A. H. and Rees, D. A. (1985).  The fine structures of guar and carob galactomannans.  Carbohydrate Research, 139, 237-260.