Rheological, Textural, and Sensorial Characterization of Walnut Butter

1. Introduction

Today, consumer awareness of unhealthy eating habits, especially the lack of natural foods, or the consumption of foods rich in saturated fats, food additives, salt, and/or sugars is observed in most societies [ 1 ]. In recent years, herbal-based butter (nut and seed butter) has been widely consumed by people around the world. Peanut butter is the most widely consumed plant-based butter [ 2 3 ], but countless varieties of butter have been developed (soybean butter, almond butter, pistachio butter, cashew butter, sunflower seed butter, pumpkin seed butter, and sesame butter, etc.) from various types of nuts and seeds, which are a good source of protein, fiber, essential fatty acids and other nutrients [ 4 ]. The development of new walnut spreads could make a significant contribution to the daily diet and present a healthier snack to consumers as they become more interested in the health, taste, and quality of food ingredients. Undoubtedly, the interest in healthy foods that meet the nutritional requirements of consumers has also brought awareness of the need for new functional products on the market.

Juglans regia

L.) is one of the main nut crops in the world, which grows in large areas in northern Bukovina (Suceava Romania). Walnuts have been harvested since prehistoric times [

Walnut (L.) is one of the main nut crops in the world, which grows in large areas in northern Bukovina (Suceava Romania). Walnuts have been harvested since prehistoric times [ 5 ], and are an important part of regular diet; the use of walnuts in bakeries and pastries is a part of cultural identity [ 6 7 ]. The use of walnuts, as an important part of our daily food, has its roots in food traditions [ 6 ]. Walnuts can be eaten raw, fried, and salted, added to dairy products, or can be sprinkled on salads, and desserts, especially walnut ice cream. Walnut desserts have been appreciated for thousands of years. One of the widespread applications of walnuts is their use in the confectionery industry by adding them to biscuits, cakes, and desserts.

8,

Walnuts are rich sources of polyunsaturated lipids (a perfect balance of polyunsaturated fatty acids (PUFA) n-6:n-3 (4:1)), proteins, dietary fiber, carbohydrates, minerals, especially potassium, magnesium, calcium, and other micronutrients; therefore, they are ingredients in different diets recommended for the prevention of aging and age-related diseases [ 7 9 ]. Nowadays, walnuts are one of the most important sources of polyphenols; the main polyphenol in nuts is pedunculagin, an ellagitannins. Ellagitannins possess antioxidant and anti-inflammatory bioactivity with a role against the onset of disease, including cancer, cardiovascular and neurodegenerative diseases [ 10 ]. Walnuts roasted with hot air to improve the sensory properties, develop the characteristic taste and aromas as well as improve the texture, have become popular snacks, and are a valuable raw material in the food industry [ 11 ]. For example, studies have revealed that the optimum roasting conditions for walnuts are 130–150 °C for 15–20 min [ 12 ], or in other research taking into account the variations of the nutritional qualities, the heat drying of 105 °C was recommended as an optimal process for walnut drying, in which protein, soluble sugar, carbohydrate, and minerals showed the highest values [ 13 ]. Walnuts can be used as spreadable pasta by people who suffer from peanut allergy. Walnut-based pasta is obtained by roasting and grinding the kernels.

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levels) on the rheological texture homogeneity (GLCMs and fractal dimension) and stability of walnut butter have been studied by Shahidi-Noghabi et al. [

Walnut butter is one of the best alternatives to milk butter; it is one of the most sustainable foods; and it is environmentally friendly, with health-promoting effects; therefore, many studies have reported its role in preventing many diseases, such as diabetes 2 [ 14 15 ], hypercholesterolemia [ 14 ], obesity [ 16 ] and coronary heart disease [ 17 ]. The effects of different levels of emulsifying agents (mono-diglyceride and lecithin at 0, 0.5, and 1.5%levels) on the rheological texture homogeneity (GLCMs and fractal dimension) and stability of walnut butter have been studied by Shahidi-Noghabi et al. [ 18 ]. They found that the oil droplet’s size of butter decreased considerably by adding an emulsifier, which was more considerable in 1.5% lecithin. Walnuts are an important food in the vegetarian diet, due to their digestible proteins and low lysine/arginine ratio, and numerous studies state that most of the necessary amino acids could be provided when nuts are eaten with legumes [ 19 ]. Previously published reports on the rheological properties of soy-butter [ 20 ], low-calorie pistachio butter [ 21 ], sesame butter [ 22 ], peanut butter [ 23 ] has been the subject of various studies primarily directed to improve its rheological and textural properties. The effects of microwave processing conditions at different roasting powers (400 W, 800 W, and 1200 W) and times (4, 4.5, 5, and 5.5 min) have already been described for peanut butter produced from four peanut cultivars, compared to those of commercial peanut butter (CPB). Peanut butter color showed the lowest brightness L* value and the highest a* values compared to the CPB [ 24 ].

Inulin, a polymer of fructose, is widely used in functional foods. The so-called prebiotic agent or undigested food supplement, and artichoke tuber contains a large amount of inulin, approx. 20%, 2% protein, a low-fat content, and significant amounts of mineral salts [ 25 ]. According to Ropciuc et al. [ 26 ], using Jerusalem artichoke as a sweetener increases the fiber content of the products and has various health benefits.

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sap) collected from certain maple species (genus

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) [

Maple syrup is a natural vegetable product that is consumed worldwide and is made entirely from tree sap. It is a natural sweetener, contains approximately 67% solids, mostly sugars, but is also rich in minerals, amino and organic acids, and a phenolic substance produced by concentrating colorless aqueous sap (sap) collected from certain maple species (genus) [ 27 ].

Products that contain at least 90% nut/seed ingredients are classified as a herbal butter (nuts/seeds), and spreads refer to a spread that has at least 40% nut ingredients that can be added in different forms [ 4 ].

The current demand for natural products requires continuous development by small producers who process walnut in various forms, including kernels, for cakes or to be added to breakfast cereals, or to produce oil by cold pressing for dressings and salads.

The present study had the following three main objectives: (1) to obtain a healthy and appreciated product, (2) to obtain information about consumer perceptions of walnut butter, and (3) to identify the main constraints in purchasing walnut butter in the North-East Region of Romania taking into account the consumers’ interest in different natural products.

Therefore, the present study was conducted to determine the stability and acceptability of walnut butter as well as the factors that influence the choice to consume this category of products. In this paper, the effect of different levels of Xanthan gum (at 0, 0.5, and 1.5, 2%

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levels) and different edulcorants (Jerusalem artichoke powder and maple syrup) concentrations on the rheological, textural, and color attributes, and stability of walnut butter were studied.