Research Report Effects of added glutamate on liking for novel food flavors John Prescott * Sensory Science Research Centre, University of Otago, Dunedin, New Zealand Received 15 September 2002; revised 28 June 2003; accepted 28 August 2003 Abstract Adding glutamate to foods increases their umami quality, their acceptability and their consumption. The functional significance of this palatability is unclear. Other highly palatable substances, e.g. sugar and fats, also increase liking for novel flavors with which they are repeatedly paired, especially when ingested. This is thought to reflect the rewarding effects of sugar and fat energy, post-ingestion. To determine if a liking for novel flavors can also be conditioned using glutamate, 44 subjects rated 10 ml samples of three novel soups for liking and familiarity, both before and after seven daily exposures to each of two soup flavors—one with added monosodium L-glutamate (MSG) (0.5% w/w; MSG þ ) and one without (MSG 2 ). During exposure, subjects received either a 250 ml bowl of soup (Consume group) or a 10 ml sample (Taste group). There were no significant differences as a function of samples or groups, despite some trends for changes in liking to be higher in the consumed MSG þ condition. In a second experiment, 69 subjects were divided into three groups (Consume MSG þ ; Consume MSG 2 ; Taste MSG þ ) in which they received nine exposures to one novel soup flavor. The Consume MSG þ group showed a significantly greater increase in liking than either the Consume MSG 2 or the Taste MSG þ groups, which did not differ. Changes in familiarity ratings reflected amount consumed, not MSG content. Pairing glutamate with a novel flavor can condition liking for that flavor. While post-ingestive effects of glutamate may be rewarding, flavor conditioning cannot be ruled out. q 2003 Elsevier Ltd. All rights reserved. Keywords: Glutamate; Umami; Preference; Flavor; Post-ingestional effects; Taste Introduction The mammalian gustatory system responds to a set of basic qualities—traditionally, sweet, sour, salty and bitter— that elicit relatively fixed hedonic responses. Many species, including humans, prefer sweetness and reject bitterness. These responses are evident from birth, or shortly thereafter, and are probably innate (Steiner, Glaser, Hawilo, & Berridge, 2001). Their origin appears to lie in the adaptive value in signalling the nutritional implications of taste qualities. The palatability of any taste compound, and the pattern of responsiveness of taste cells in the rat brainstem, is inversely related to its toxicity (Scott & Mark, 1987). Highly toxic compounds are rejected as unpalatable, primarily due to bitterness; highly nutritive substances with low toxicity are preferred, mainly because they are sweet. This neural and behavioral organisation has led to the hypothesis that preferences for tastes are a means by which physiological wellbeing is maintained (Scott, 1992). Consistent with this, metabolic states can modulate taste palatability—preferred levels of salt in foods increase following salt depletion (Beauchamp, Bertino, Burke, & Engleman, 1990), while sweetness becomes less pleasant following glucose consumption (Cabanac, 1971). Glutamate, derived from the non-essential amino acid, glutamic acid, is an important contributor to food flavors. The addition of sauces (soy; Worcestershire), cheese (especially Parmesan), tomatoes, mushrooms, or meat, fish and vegetable stocks to foods all have the effect of increasing glutamate levels (Ninomiya, 1998; Yamaguchi, 1991). Since early 1900s, monosodium L-glutamate (MSG) has been commercially manufactured for use as a flavor enhancer, and there is ample evidence that adding MSG to suitable foods increases their palatability (Bellisle et al., 1991; Yamaguchi & Takahashi, 1984a,b) and consumption (Bellisle, 1998; Rogers & Blundell, 1990; Schiffman, 1998). Such hedonic changes are probably partly mediated by changes in the sensory properties of the foods, including increase in richness, savouriness and mouthfeel qualities (Fuke & Shimizu, 1993; Prescott, 2001; Yamaguchi, 1991). 0195-6663/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.appet.2003.08.013 Appetite 42 (2004) 143–150 www.elsevier.com/locate/appet * Address: School of Psychology, James Cook University, Cairns, Qld 4870, Australia. E-mail address: john.prescott@jcu.edu.au (J. Prescott).