Characterising the sensory profile of walnut kernels using a Napping method combined with free text description

Abstract

New Zealand's walnut sector has been rapidly growing since 1970. Exciting opportunities have been identified in cultivar development, export market perspectives, premium products and low carbon emissions related to growing. The walnut kernel is the main product of the sector. Growers would like to see the sensory uniqueness of their products using a convenient assessment. This study aimed to develop a rapid sensory method to profile walnut kernel products. 9 walnut kernel products were sensorily evaluated with 20 semi-trained participants during a 2-hour session. A modified Napping was performed where participants were asked to group the samples based on their overall similarity, and then exhaust the sensory attributes and hedonic terms they perceived from each sample in a free text form. The free text was cleaned, destemmed and converted into a term-frequency table. The Napping coordinate and term-frequency table were analysed by a Procrustean Multiple Factor Analysis (PMFA) to generate a compromised product-attribute map. The results show that the walnuts were clearly differentiated in the map based on several key sensory attributes including visual brownness, rancidity smell, nutty flavour, roasted flavour, bitter taste, astringency texture and oiliness texture. It is concluded that Napping method can differentiate the walnut kernels efficiently while providing insights into the direction of difference in attributes. The walnut industry can easily adopt this method for in-house profiling. The next step will be linking physicochemical measurement to the sensory results and finding out the key drivers of their distinct sensory characteristics.