Jacobs, J., Kratsch, H., Omaye, S., and Treftz C. 2016, Nutritional and Sensory Analysis of Raspberry Varieties Grown in Northern Nevada, University of Nevada Cooperative Extension, Special Publication 16-14

Berries are an excellent source of vitamins and antioxidants, and have been grown successfully in other high-desert regions of the U.S. We investigated the nutritional and sensory qualities of different raspberry varieties grown in northern Nevada. This information will help growers in Nevada to select and produce raspberry varieties with the greatest potential for commercial success.

Introduction

Berry fruits have been promoted for their many health benefits. Benefits include antioxidant activity, lowered risk of heart disease and other obesity-related diseases, and lowering risk of certain types of cancers. Raspberries are high in vitamin C, vitamin E and other antioxidants.

Previous research on raspberry nutrition has focused on European raspberry varieties or on varieties from the midwestern or southern United States. These studies show wide variations in vitamin and mineral contents. Little is known about antioxidant content of raspberries grown in dry regions. Raspberries grown in dry regions are thought to have less moisture but may be otherwise similar to berries grown in other regions of the world. A study conducted in Utah showed differences among several primocane raspberry cultivars (Freeman et al., 2011).

In northern Nevada, extreme temperatures limit food production in the summer and winter. Despite this limitation, consumers in Nevada and elsewhere are becoming interested in the health benefits of eating fruit and the farm-to-table benefits of locally grown produce. To our knowledge, no studies have looked at nutritional or sensory quality of raspberries grown in northern Nevada. The purpose of this study was to measure vitamin C, vitamin E, total polyphenolics (antioxidants) and sugars (glucose and fructose) in several raspberry varieties during two growing seasons and during different months of harvest. We hypothesized these nutrients would vary across types, as well as harvest month. We also measured taste preferences for three raspberry varieties. Our results can be used to inform potential berry farmers in dry climates about the nutritional qualities and consumer preferences for raspberries.

Methods

Raspberry growing conditions

Raspberries were planted in 2012 at Jacobs Family Berry Farm, Gardnerville, Nevada. All plants were drip irrigated every other day, three times per day. Berries were supported by a V-trellis system. Berries were pruned according to variety. Floricane varieties (Jewel, Encore and Nova) were pruned in early spring to remove all previous year canes, except the six to eight best. The tops were cut to 4 to 5 feet high, and the laterals were cut to 4 to 7 inches. Primocane varieties (Polana, Jaclyn, Joan J and Heritage) were cut to within 1 to 2 inches of the ground in early spring.

For all varieties, the new canes were tipped in summer when they reached 4 to 5 feet to encourage lateral growth. Plants were thinned by removing the laterals on the lower 18 inches to open up the plant; new canes that had emerged outside the row were removed to maintain a row width of 12 to 18 inches. After harvest, the fruiting canes were removed.

Nutrient analysis

Materials, equipment and procedures have been described previously (Treftz & Omaye, 2015). Raspberries were harvested in June, July and August during 2013 and 2014. At Jacobs Family Berry Farm, raspberries were harvested when they reached 100 percent visual red (or black, depending on variety) surface color between 7 a.m. and 8 a.m. The berries were placed in tubes and then on dry ice in a cooler. The raspberries were transported to the University of Nevada, Reno and immediately stored in a freezer until ready for nutrient analysis. Berries were randomly selected for analysis by hand. They were rinsed with water to remove dirt and allowed to dry on a paper towel.

Sensory analysis

Participants were recruited through undergraduate food science classes at the University of Nevada, Reno (N=76). This study was approved by the University’s Institutional Review Board (project number: 583149-1). Participants were not trained in sensory evaluation and were asked to give their taste preferences on locally grown berries. Sensory evaluation was conducted at the sensory laboratory on campus. The sensory laboratory was designed according to the American Society of Testing Materials standards and was built with an 11-inch sliding door. Raspberries were sampled within two days of harvest, and all data were collected during September 2013. Raspberries were rinsed with tap water, allowed to dry on a paper towels and served at room temperature in 2-ounce clear plastic cups. The students were asked to rank their preferences for three different berries on 13 taste attributes using a 5-point scale. The scale used smiley faces, ranging from ‘very satisfied’ to ‘very unsatisfied’ (Beckley, Moskowitz, & Resurrection, 2006).

Statistical analysis

Statistical analysis was conducted using IBM SPSS Statistics software, version 22 (Armonk, New York). We used ANOVA to compare overall variations in nutrient parameters, followed by Tukey’s post-hoc tests to compare across harvest dates. For varieties with two harvest dates, the independent t-test was used. For sensory analysis, ANOVA was used to compare scores, followed by Tukey’s post-hoc tests. The significance level was set at p<0.05. Results are expressed in mean ± standard deviation.

Results

Results for the sensory analysis portion of the study are outlined in Table 1. Out of the 13 sensory attributes assessed, aroma intensity, sweetness, fruit juiciness, overall taste and overall flavor showed significant differences. Jaclyn aroma intensity ratings were higher than Polana. Jaclyn was rated higher for sweetness, fruit juiciness and overall taste and flavor, compared to Polana and Heritage.

Table 1. Sensory analysis across raspberry varieties*.

*table here

Means within a row followed by the same letter are not different according to Tukey’s honest significant difference at p<0.05 (N=18). *5=very satisfied, 4=satisfied, 3=neutral, 2=unsatisfied, 1=very unsatisfied.

Nutrient analysis results for Encore variety are listed in Table 2. The results indicated significant differences across harvest dates for all nutrients except fructose. The highest vitamin E and total polyphenolic compounds were observed in July 2013. The highest amounts of fructose and glucose were observed in August 2013.

Table 2. Encore raspberry nutrient analysis across harvest dates.

*table here

Means within a row followed by the same letter are not different according to Tukey’s honest significant difference at p<0.05.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

Results for Joan J are shown in Table 3. The highest amounts of vitamin C were found in September 2014, vitamin E content was highest in August 2014, total polyphenolics content was highest in August 2014, fructose content was highest during September 2013 and glucose was highest in September 2014.

Table 3. Joan J raspberry nutrient analysis across harvest dates.

*table here

Means within a row followed by the same letter are not different according to Tukey’s honest significant difference at p<0.05.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

The results for Nova are outlined in Table 4. The highest levels of vitamin E, Brix and fructose were seen in August 2013. The highest levels of total polyphenolics were seen in July 2014. Jewel results are outlined in Table 5. Differences were observed among harvest dates for vitamin E, with higher results observed in July 2013. Table 6 outlines the results from Polana. Results varied between the harvest dates of September 2013 and September 2014 for all measurements except Brix. Also comparing September 2013 with September 2014, Heritage raspberries (Table 7) indicated significant 5 differences among vitamin C, fructose and glucose levels. Table 8 outlines results from Jaclyn. The greatest differences were between the 2013 and 2014 harvest dates; however, differences were also seen among different months of the same year.

Table 4. Nova raspberry nutrient analysis across harvest dates.

*table here

Means within a row followed by the same letter are not different according to Tukey’s honest significant difference at p<0.05.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

Table 5. Jewel raspberry nutrient analysis across harvest dates.

*table here

p value calculated using independent t-test.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

Table 6. Polana raspberry nutrient analysis across harvest dates.

*table here

p value calculated using independent t-test.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

Table 7. Heritage raspberry nutrient analysis across harvest dates.

*table here

p value calculated using independent t-test.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

Table 8. Jaclyn raspberry nutrient analysis across harvest dates.

*table here

Means within a row followed by the same letter are not different according to Tukey’s honest significant difference at p<0.05.

*mg/100g berries

**g/100g berries

***Brix is a measure of the percent solids in an aqueous solution, most often referring to sugar content.

Discussion

This is the first time a nutritional analysis has been conducted on raspberries grown in northern Nevada. Similar to the previous study conducted with raspberries grown in high-desert growing conditions, variations were seen among varieties. Differences among vitamins, sugars and harvest dates were dependent on variety of raspberry and harvest date. Since not all raspberries were available at every harvest date, results cannot be easily compared among varieties. In general, it was observed that the greatest differences were among harvest years, and smaller differences among nutrients were observed among harvest months within the same years. This study did not control for environmental variation between harvest years, and such differences are likely the result of factors known to affect nutritional qualities of the fruit.

Sensory analysis data showed that untrained consumers preferred the Jaclyn variety compared to Heritage and Polana, with preferences for sweetness, overall taste and fruit juiciness. However, sugar 7 content of these varieties was not different. Although differences in vitamin C content among varieties could not be analyzed statistically due to harvest date differences, vitamin C content was observed to be highest in the Jaclyn variety, which could potentially be contributing to the participants’ observed taste differences.

Eating food grown locally has several benefits, from economic growth of the local economy to environmental and nutritional benefits. Growing raspberry fruits in high-desert climates has the potential to provide nutritionally dense and attractive fruits to the local population.

Authors

  • Chenin Treftz*, Graduate Assistant Heidi Kratsch*,
  • Jacobs Family Berry Farm
  • Stanley Omaye*, Department of Agriculture, Nutrition and Veterinary Sciences*

Literature Cited

Beckley, J.H., Moskowitz, H.R., & Resurreccion, A.V. (2006). Sensory and Consumer Research in Food Product Design and Development. Blackwell Publishing. Doi:10.1002/9780470277706

Freeman, B.L., Stocks, J.C., Eggett, D.L., & Parker, T.L. (2011). Antioxidant and phenolic changes across one harvest season and two storage conditions in primocane raspberries (Rubus idaeus L.) grown in a hot, dry climate. HortScience, 46(2), 236-239.

Treftz, C., & Omaye. S.T. (2015). Nutrient analysis of soil and soilless media strawberries and raspberries grown in a greenhouse. Food and Nutrition Sciences, 6, 805-815.

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