The effect of high-polyphenol sumac on food intake in younger and older adults, using sensory and appetite analysis

Ageing sees a decline in appetite and food intake with associated deficiencies in both macronutrients and micronutrients. Reduced food intake will eventually lead to malnutrition. Different factors may contribute to malnutrition, including the physiological condition of a person, such as smell or taste dysfunction. Research has investigated methods that help to increase food consumption in the older population, with some studies demonstrating the impact of added herbs and spices on improving the liking and palatability of food. Spices with high polyphenol and antioxidant activity exhibit various health benefits, including regulating blood glucose levels. Moreover, monosodium glutamate (MSG) has been added to different foods, resulting in flavour enhancement and increased appetite. Hence, it can be hypothesised that sumac, containing glutamic acid, in addition to its high antioxidant and polyphenol content as a potential natural flavour enhancer, might also increase appetite among older adults. This PhD study aimed: (1) to determine the antioxidant activity (mol/ L), polyphenol content (mg GAE/g) and glutamic acid level (g glutamic acid/100g protein) of two forms of sumac (fresh and commercial) from four regions (Turkey, Palestine, Iran and the UK), in two colours (red and brown), using three solvents (water, acetone 80% and ethanol 80%); (2) to assess the acceptability and liking of different doses (0%, 0.25%, 0.5%, 0.75% and 1%) of sumac among free-living older and younger adults; (3) to evaluate food intake following the consumption of sumac (1%) in vegetable soup – during an ad libitum lunch, a main evening meal and an all-day – among free-living older adults , younger adults and older adults living in residential nursing homes. The food intake of older adults in residential nursing homes was assessed based on an ad libitum lunch and all-day data. Soup samples were compared based on different methods for the addition of sumac: sumac during (SSC) and after cooking (SSE), along with a control soup (SC) with no sumac added. To evaluate the polyphenol content and antioxidant activity of the sumac samples, a Folin-Ciocalteu assay (FCR) and ferric ion reducing antioxidant power (FRAP) were used, respectively. L-glutamic acid was assessed using a Megazyme L-glutamic assay. Compusense (Compusense Inc., Ontario, Canada) software was used to assess the sensory evaluation attributes of free-living older adults (over 65 years old) and younger adults (18–35 years old) receiving different doses of sumac in butternut squash soup. Nutritics software was used to assess food intake following the addition of 0.37g of sumac to soup. This study demonstrates that fresh brown sumac (FBS) had the highest levels of antioxidants (water: 14.1±4.9, acetone 80%: 14.2±2.1 mol/L), polyphenols (water: 2.4±1.3, acetone 80%: 5.4±5.3 and ethanol 80%: 3.4±1.4 mg GAE/g) and L-glutamic acid (8.7±0.2 g glutamic acid/100g protein). Following the FBS sample, commercial Iranian brown sumac (CIBS) had the next highest antioxidant (water: 9.1±2.7, acetone: 13.9±2.1 and ethanol: 27.6±6.3 mol/L), polyphenol (water: 1.5±0.7, acetone: 5.1±4.8 and ethanol: 2.7±0.6 mg GAE/g) and L-glutamic acid (5.2±0.3 g glutamic acid/100g protein) levels. A positive correlation coefficient was observed between polyphenol and antioxidant activity in water (r=0.66, p=0.001), acetone 80% (r=0.787, p=0.001) and ethanol 80% (r=0.388, p=0.001). Sensory evaluation results revealed that the intensity of the brown colour between the soup samples and control soup was greater in the younger adults group (χ2(4) = 23.5; p=0.001) than free-living older adults (χ2(4) =10.2; p=0.037). Other attributes did not show any statistical differences; however, the highest dose of sumac in soup received the highest ranking for overall liking acceptance by both groups of adults compared with the other samples. This study found that during the ad libitum lunch, free-living older adults consumed more energy (kcal; χ2(20) = 8.6; p=0.014), protein (g; χ2(20) =7.4; p=0.025), carbohydrate (g; χ2= (20) =8.7; p=0.013) and fat (g; χ2(20) =12.6; p=0.002) in sumac added at the end (SSE), and sumac contributed to soup (SSC) sessions compared to control session (SC). The outcome of a pairwise comparison confirmed that the two methods of adding sumac (SSE and SSC) compared with the control session (SC) had no impact on food intake (p>0.05). The evening meal outcome showed younger adults had a higher intake of protein in the SSC session compared with free-living older adults (t (38) = 10.02; p=0.003). In continuation to the assessment of both groups of adults, all-day protein intake was significantly higher in younger adults compared with free-living older adults in both SSE (t (38) =0.54; p=0.006) and SSC (t (38) =1.72; p=0.004) sessions. The influence of the addition of sumac following the SSE and SSC sessions among residential older adults demonstrated a borderline difference in the carbohydrate (F(2,8) = 0.558; p=0.049) intake of the ad libitum lunch. However, a pairwise comparison demonstrated no differences between test sessions (p>0.05). Thus, the overall findings of this thesis suggest that the addition of sumac to food may have a potential benefit for ad libitum lunch intake, leading to a more effective strategy for managing malnutrition and increasing healthy ageing, which can contribute to reductions in cost and concern for public health