Abstract
L‑glutaminase (L‑glutamine amidohydrolase EC3.5.1.2) is the key enzyme in enhancing the taste and aroma of oriental fermented foods by increasing their glutamic acid content and as a result imparting a palatable taste. Beef burgers were prepared using different levels of the partially purified L- glutaminase (2.0 to10.0 U/100 g) prepared from Aspergillus oryzae NRRL 32567. Beef burgers treated with 6.0 U/100g and the others treated with monosodium glutamate (5000 ppm) were chemically, sensory and microbiologically evaluated and compared to untreated control during frozen storage at –18 ºC for 3 months. Treatment with L‑glutaminase (6 U/100g) resulted in an increase of 443% in glutamic acid and a reduction of 63% in glutamine contents resulting in an enhanced preferable taste and odor of the prepared beef burgers. Burgers treated with 6.0 U/100g exhibited the best odor, texture, taste and overall quality scores when compared to the untreated control and samples treated with monosodium glutamate (5000 ppm). During the frozen storage of all samples, an expected slight, but significant (p≤0.05), increase in the total mesophilic bacterial count was evident and such increase was quite acceptable since numbers did not exceed the limit of 5.7x103 cfu/g. Similarly, the total psychrotrophs did not exceed 3.7x102 cfu/g.
Highlights
L-Glutaminase (L‐glutamine amidohydrolase EC3.5.1.2) catalyzes the hydrolysis of L‐glutamine to L‐glutamic acid and ammonia [1,2]
The hydrolysis of meat proteins generates polypeptides that can be further degraded to smaller peptides and free amino acids
Results clearly show an increase in the amount of glutamic acid from 23 to 125 mg/100 g and a decrease in glutamine content from 119 to 75 mg/100 g in the control and treatment B samples, respectively
Summary
L-Glutaminase (L‐glutamine amidohydrolase EC3.5.1.2) catalyzes the hydrolysis of L‐glutamine to L‐glutamic acid and ammonia [1,2]. Amino acids that are produced by the enzymatic degradation of the proteins contained in the raw materials are well known as basic flavor components of fermented condiments. L‐glutamic acid is one such flavor enhancing amino acid produced by the hydrolytic action of L‐glutaminase on L‐glutamine [6,7]. Monosodium glutamate (MSG) gives the taste “umami”, which has been widely recognized as the fifth basic taste besides sweet, acid, salty and bitter. It has been widely used as a flavor enhancer in the food industry. Glutamic and aspartic acids are well known amino acids contributing fine taste, “umami” and sharp sour taste and nutritional effects to food [10,11]. The effect of such replacement on the chemical, sensory and microbiological quality of the produced burger were evaluated
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