Written by Sara Serra, WSU, March 2019
Evaluating the fruit dry matter at harvest by the adoption of a NIR (near-infrared spectroscopy) technology can contribute to increase consumer pear liking. The dry matter metric, as its name suggests, is what is left over in the fruit after all the water is removed such as fibers, proteins, acids, starch, and sugars. As the fruit grows on the tree, it accumulates starch from photosynthesis which is later converted to sugar during the cold-storage and ripening period. Thus, measuring dry matter at harvest is a reliable indicator of future eating quality as dry matter includes both sugars as well as starch that evolves in to sugars during storage and ripening. Additionally, since dry matter accounts for many other fruit properties and not just starch and sugar, it may be uniquely equipped to characterize the flavor potential of the fruit as well.
While dry matter is traditionally obtained by drying a fruit sample in an oven, emerging research has shown near-infrared spectroscopy to be a reliable tool in assessing dry matter non-destructively, keeping the fruit intact and viable for market. By correlating light energy absorbed by the fruit to known parameters, near-infrared spectroscopy can rapidly and accurately determine internal fruit properties such as dry matter, enabling fruit quality characterization of an entire harvest with the potential to establish minimum quality standards or even premium-quality fruits (Fig. 1).
Building off of previous work establishing a proof-of-concept of near-infrared spectroscopy to predict dry matter in pears, horticulture researchers Drs. Stefano Musacchi and Sara Serra and research assistant Alex Goke paired with WSU School of Food Science researcher Dr. Carolyn Ross to investigate whether sorting d’Anjou pears by dry matter at harvest could increase consumer satisfaction after cold storage and ripening. Using the classifications of low (< 13 %), moderate (13 – 16 %), and high (> 16 %) dry matter, d’Anjou pears were presented to a large body of typical (untrained) pear consumers who were asked to evaluate the fruits in terms of their liking of sweetness, flavor, and overall liking as well as the price they were willing to pay for a fruit of that dry matter level at the grocery store. In total, 3,886 fruit samples were evaluated, representing two commercial orchards harvested in 2016 and 2017.
Consumers prefer high dry matter fruits over moderate and low dry matter fruits in nearly all attributes evaluated (Fig. 2). Most notably, sweetness, flavor, and overall liking (Fig. 3) were significantly higher in high dry matter fruits relative to moderate and low dry matter fruits. This suggests that sorting fruit by dry matter can create high quality, low variability groups of fruit to satisfy consumer demands by removing low quality (low dry matter) fruits from the market. This was further reflected in the price consumers were willing pay for high dry matter fruits. On average, consumers were willing to pay $0.20 more per pound than the average price of fresh pears categorized as high dry matter, and $0.13 more per pound for moderate dry matter fruit (Fig. 4).
Together, these results indicate that dry matter is a useful metric for classifying pears at harvest in to dry matter categories that yield consistent, high quality eating experiences. While this work was conducted using a handheld NIR device (Felix F750 Produce Quality Meter) to capitalize on its portability and ease of use, sorting fruit for dry matter and maximum consumer satisfaction could be readily implemented at production scale here in the Pacific Northwest as many operators have begun to upgrade their packing lines to include NIR optics.