Commercialization of Hazelnuts for Growers in the Upper Midwest

Outcome 1: On-Farm Evaluation of Select Hazelnut Genotypes

Production of Liners

We propose to contract with Knight Hollow Nursery of Middleton, WI to utilize their hazelnut micropropagation experience to generate rooted clonal liners of each of four genotypes for planting at each of fifteen farms and at two University research stations.  Collaborating growers will purchase liners for either a Genotype (50 liners) or Agronomic Trial (200 liners) and contribute all labor and resources necessary to establish the trials.  Five-hundred (500) liners will be produced for each of two research station plantings for agronomic trials to follow up on questions raised by current agronomic trials, including but not limited to weed management, fertilization, irrigation and pruning.

Fall 2015 – Eight genotypes from the replicated hybrid performance trials were selected based on the 2013 and 2014 yield and performance data from the St. Paul and Bayfield trials.  Rooted shoots from each of these genotypes were dug in the fall of 2014, transplanted into pots, and grown in a greenhouse.  Four of the eight genotypes will be chosen for propagation based on the 2015 yield data and the success of getting the genotypes into culture.

Winter2015/Spring 2016 – The potted stock plants will be brought out of dormancy, then plant hormones and shoot tip pruning will be used to rejuvenate them and encourage production of new shoots.  The shoot tips will be harvested and cultured on agar medium with hormones and nutrients per the protocol developed by Knight Hollow Nursery. 

Summer/Fall 2016 – The rooted plantlets will be harvested and transplanted into soil-less potting mix for continued growth and acclimation.

Winter 2015/2016 – The plants will be greenhouse-grown through the fall, allowed to go dormant in early winter and transplanted while still dormant in spring 2017. 

Trial Plantings

The research plantings will be established at the Spooner Agricultural Research Station in Spooner, WI and the Horticultural Research Center in Chanhassen, MN.  The on-farm Genotype and Agronomic Trials will be established and managed by 15 growers participating in the Hazelnut Improvement Program.  Participating growers have agreed to conduct all site preparation, establishment, and management at their own expense.  In addition, the growers have agreed to purchase the plants at cost.  The cost shall be the expenses incurred by Knight Hollow to produce the liners in excess of the costs covered by this grant project.  Growers have been chosen based on interest and their record of managing plantings, and with a goal of representing a diverse range of environments.

Summer/Fall 2016 – Jason Fischbach, Lois Braun, or the hired field technician will visit each participating grower to develop and implement a site preparation plan.  Site preparation at each site will be completed by freeze-up in 2016.

Spring 2017 through Oct 2018 - The plants will be established in the spring of 2017 and maintained for optimum growth in order to quantify performance.  The two research station plantings, and the on-farm Agronomic Trial plantings will be used for agronomic trials including weed management, fertilization, irrigation and pruning as determined by the interests of the grower and demands of the site.  Such trials have so far been confounded by lack of genetic uniformity with the trial plants.

Outcome 2: Optimizing Post-Harvest Handling for Processing

Equilibrium Moisture Content (EMC) Determination of Nuts and Nut Clusters

Saturated salt solutions are commonly used to determine the equilibrium moisture content of materials.  At UW-Madison, unique equipment for more rapidly reaching equilibrium moisture content in a saturated salt solution environment has been developed.  This equipment will be used to establish EMC curves for hazelnuts and hazelnut clusters (i.e., unhusked nuts).  Such curves allow for modeling expected moisture content in response to different drying methods, saving the need for expensive drying experiments.  A minimum of six different salt solutions will be used at three different temperatures (40F, 80F, and 120F).  Original moisture content of the nuts and nut clusters will be determined using standard ASTM procedures.  Nuts and nut clusters will then be put into EMC chambers and weighed daily.  Temperature and relative humidity within EMC chambers will be recorded on 10 minute intervals.  Once daily weighing shows that EMC has been attained, a sample of nuts and nut clusters will be removed from each chamber for moisture content determination.

Physical Properties of Hazelnuts

Nuts conditioned to six different moisture contents will be loaded at room temperature between two parallel plates to determine the specific deformation, bio-yield force, rupture force, and rupture energy required to initiate shell and kernel rupture Tests will be carried out at deformation rates of 0.5 inches per min and 10 inches per minute.  One-third of the nuts will be loaded in the X-direction (X-axis is the longitudinal axis through the hilum), one-third in the Y-direction (Y-axis is the transverse axis containing the major dimension at right angles to the longitudinal axis), and one-third in the Z-direction (Z-axis is the transverse axis containing the minimum dimension). Physical characteristics of the nut (mass, dimensions, geometric mean diameter, sphericity, moisture content (MC), the broken shell (thickness, surface area, MC) and kernel (mass, dimensions, geometric mean diameter, sphericity, MC) will be determined.  Nuts taken from the same conditioned batch of nuts as those loaded to failure in this study, will also be ran through two different cracking machines to obtain relationships between commercial and laboratory cracking processes with the goal being to determine the combination of moisture and cracking method yielding the least amount of damage to the kernels.

Outcome 3: Optimizing Post-Harvest Handling for Flavor

We will develop a comprehensive molecular fingerprint of hazelnut flavor quality as influenced by post-harvest handing condition to provide the know how to maintain high product acceptability and freshness.  The first step will be to define the principal compounds responsible for flavor and, more importantly, compounds that impart negative flavors.

Taste compounds will be identified based on methods developed by Jiang and Peterson (2013). Ethanol/water extracts will be optimized for taste isolation.  The subsequent isolate will be fractionated by ultra-filtration and further screened for taste-activity. The fractions identified as taste-active will be fractionated by off-line 2D high-pressure liquid chromatography and purified peaks will be screened for taste activity. The intensity of the taste active fractions will be determined by sensory analysis and used to select compounds that contribute the most to taste. The key taste-active compounds will be structurally elucidated using advanced analytical techniques (i.e. LC/MS-Qtof, NMR). The target taste compounds will be quantified by LC/MS/MS techniques.  Taste recombination studies will be conducted for validation of the taste active compounds selected. The chemical nature of the identified off-flavor compounds will provide insight into the mechanisms of formation (enzymatic or non-enzymatic) and provide a basis to optimize post-harvest handling procedures to maintain maximum nut quality.  In future would we can further extrapolate this molecular flavor map to additional samples to further investigate the influence of growing region or cultivar on flavor performance. 

Effects of post-harvest drying methods.

Using the EMC curves and the optimal moisture content for cracking, three different husk-drying regimes will be evaluated to achieve the desired moisture content: 68F, 68F with forced air, 130F with forced air.  In the fall of 2016, all in-husk nut clusters will be harvested from at least two plants of each of 10 separate genotypes.  The clusters will be placed in 1 gallon plastic mesh onion bags with three bags per drying treatment (9 gallons/genotype). A subsample from each bag will be husked and the moisture content of the in-shell nuts will be measured. The three husk-drying treatments will be implemented until the target moisture content is reached.  The nuts from each treatment will be rated for occurrence of shell fissures and then cracked to immediately remove the kernels for storage at -80C for chemical analysis.  Dr. Peterson’s lab will then use comprehensive analytical sensory-guided fractionation techniques coupled with LC/MS and NMR methods for compound structural elucidation to compare the levels of anti-quality flavor components in these samples.

Effects of storage conditions and duration.

In the fall of 2015, nuts will be harvested from three genotypes, dried with 68F forced air, and husked. 200 gram sub-samples of the in-shell nuts from each of the 3 genotypes will be stored in an un-insulated shed with no temperature regulation or in a climate controlled unit at a constant temperature of 68F, 35F, or 0F.  A sub-sample from each sub-sample will be removed at 30 days, 90 days, and 180 days, cracked, and the kernels will be stored at -80C for chemical analysis.  Again, Dr. Peterson’s lab will then compare the levels of anti-quality flavor components in these samples.

This work will result in optimized post-harvest handling procedures and an understanding of hybrid hazelnut flavor chemistry for use in subsequent food processing.

Outcome 4: Screening Hazelnuts for Phenolic Content and Novel Compounds

The extract of phenolics and antioxidant activity will be exploratory in nature, in an effort to determine if additional research is warranted. Phenolics in the nutmeat, involucres, shells, and leaves from 8 hybrid genotypes and 5 American genotypes will be analyzed.  Phenolics will be extracted using methods of Shahidi et al. (2007).  Briefly, samples will be ground and fats will be removed with hexane.  Extraction of phenolics will be completed using a mix of ethanol and water and then vacuum dried and stored.  Samples will be rehydrated and analyzed using HPLC.  Antioxidant activity will be assessed using a surrogate of hydrogen peroxide scavenging activity (Shahidi et al. 2007).  Briefly, hydrogen peroxide will be added to the hazelnut extracts and a spectrophotometer will be used to model the degradation of the peroxide in the samples (caused by the extracts).  Levels of phenolics and antioxidant activity will be compared to values found for C. avellana by Alasalvar et al. (2007), Contini et al. (2008) and Delgado et al. (2010). The analysis will be done at the Wisconsin Institute for Sustainable Technology.