Guar Gum as a hidden source of Glutamate
Guar gum, the powdered endosperm from the seeds of the legume Cyamopsis tetragonolobus, is a polysaccharide galactomannan (carbohydrate) fiber that contains 2.5-4.5% of a proteinaceous component. Data presented for 11 bulk commercial samples show that of the protein fraction, the most abundant amino acids are glycine, glutamic acid, aspartic acid, serine, and alanine, respectively.” 
Put another way; guar gum is 97.5% – 95.5% carbohydrate, 5% protein, and of that protein, 25-50% depending on the source, is likely to be glutamic acid. That said, because it is in a polysaccharide galactomannan fiber, the protein content is enmeshed and inter-dispersed within the carbohydrate matrix.
Guar gum is used as a thickener, and due to its high molecular weight and high viscosity, not much is needed in most cases, and very little is customarily consumed. So in the instance of a 5-gram addition of guar gum in a product, you would expect to see 0.075- 0.125 grams of glutamic acid.
5 grams of guar gum
4.75- 4.85g are carbohydrate
0.15g-0.25g are protein
0.075g -0.125g are glutamate
However, it’s worth noting again that due to the galactomannan polysaccharide matrices of guar gum, and the fact that humans do not produce polysaccharidase to enzymatically break down this fiber, it largely remains an intact soluble fiber that is primarily fermented in the distal colon. For this reason, you may expect to see around 10% bioavailability of that amount, which would result in something closer to:
0.0075 g -0.0125 g estimated bioavailable glutamate
But let’s consider guar gum and glutamic acid in the context of other common foods. To begin, let’s note that glutamates are in nearly every food we eat, and it is of the most abundant of the amino acids in the human body. In addition to its role in protein structure, it plays critical roles in nutrition, metabolism, and signaling within the central nervous system. 
Long-simmered bone broths develop deeper savory flavors, and more natural glutamates are created by heat-based cooking. Consider the following study that measured 15 samples for beef, chicken, and turkey bone broth analysis to detect amounts of various amino acids, including glutamate  :
2.576 ± 0.040% glutamate content in Beef Bone Broth
3.473 ± 0.074% glutamate content in Chicken Bone Broth
4.185 ± 0.079 % glutamate content in Turkey Bone Broth
Thus, in the context of a bone broth product with 240 grams or 1 cup per serving, each serving of beef, chicken, or turkey bone broth would render approximately:
6.24 g of glutamate in Beef Bone Broth
8.64 g of glutamate in Chicken Bone Broth
10.32 g of glutamate in Turkey Bone Broth
But let’s consider another source of “hidden” glutamate: Apples.
Apples are widely considered to be one of the safest foods for individuals wanting to avoid glutamate in their diet. The highest relative concentration of glutamic acid observed in a study of apples found 9.99 ± 0.005% in the highest (Winesap), and 2.30 ± 0.04% of the total amino acids in the lowest (Granny Smith). This almost sounds like something to be concerned about until you realize that the protein content of a 133g apple is 0.3g.. Thus, a 133g apple contains:
129.7 g carbohydrate
0.3g of protein
0.03g of glutamate
On a gram per gram basis, the apple contains 0.023% of glutamic acid. On a gram per gram basis, guar gum contains 1.5%-2.5% glutamate. On a gram per gram basis, beef, chicken, and turkey bone broth contain 2.6%, 3.6%, and 4.3%, respectively. While it is clear that on a gram per gram basis that the apple has far less glutamic acid than guar gum, and that bone broths contain somewhat similar amounts of more glutamate, the customary amounts consumed drastically change the perspective of the issue. Let’s consider the glutamate content of these various foods in the context of customarily consumed amounts:
Apple: 133 grams = 0.03g glutamate
Guar Gum: 5 grams = 0.075g -0.125g glutamate
Beef Bone Broth: 240g = 6.24g glutamate
Chicken Bone Broth: 240g =8.64g glutamate
Turkey Bone Broth: 240g = 10.32g glutamate
IS GUAR GUM A HIDDEN SOURCE OF GLUTAMATE?
Consider that the glutamate in customarily consumed amounts of guar gum is closer to that of the negligent amount in apples, and significantly less than various bone broths. Discussing the “hidden glutamate” in guar gum outside of the context of customarily consumed amounts would be at best potentially misleading to consumers, and at worst a complete misrepresentation and fearmongering of an incredible functional fiber. Only 30g per day of guar gum would meet the daily recommended requirements of soluble fiber intake. 
It should also be noted, studies evaluating the prebiotic nature of guar gum often suggest the implementation of initiatives to fortify processed foods with prebiotic guar gum, calling it a “miracle therapy for hypercholesterolemia, hyperglycemia, and obesity.” In clinical studies, guar gum has been found to reduce cholesterol, appetite, inhibit glucose absorption , aid in weight loss, acutely reduce postprandial blood glucose, reduce total serum cholesterol and triglycerides, reduce the risk for metabolic disease, and has anti-obesigenic activity. 
In effect, the addition of guar gum is beneficial, and there should be serious efforts to fortify foods in the next coming years, given the growing focus on the microbiome.
That said, this sort of thing is not new. I can’t tell you how often I’ve seen something parroted within the health and wellness sphere that was absolute bullshit. Many “reputable” sources repeat the same things without bothering to ensure that what they regurgitate has any scientific or logical basis. If you’d like to see a case in point of dozens of the world’s foremost “experts” in nutrition blatantly copy/paste misreporting on the 19 gluten cross-reactive foods without scrutiny, here is this phenomenon elucidated perfectly. 
And it appears that rampant misreporting without scrutiny in the case of guar gum being a hidden source of glutamate is also what has occurred here.