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Research Project: New Sustainable Processing Technologies to Produce Healthy, Value-Added Foods from Specialty Crops

Location: Healthy Processed Foods Research

Title: Preservation of spinach by isochoric (constant volume) freezing

item Bilbao-Sainz, Cristina
item Sinrod, Amanda
item Dao, Lan
item Takeoka, Gary
item Williams, Tina
item Wood, Delilah - De
item Bridges, David
item POWELL-PALM, MATTHEW - University Of California
item UKPAI, GIDEON - University Of California
item Chiou, Bor-Sen
item Wu, Vivian
item RUBINSKY, BORIS - University Of California
item McHugh, Tara

Submitted to: International Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2019
Publication Date: 11/28/2019
Citation: Bilbao-Sainz, C., Sinrod, A., Dao, L.T., Takeoka, G.R., Williams, T.G., Wood, D.F., Bridges, D.F., Powell-Palm, M., Ukpai, G., Chiou, B., Wu, V.C., Rubinsky, B., McHugh, T.H. 2019. Preservation of spinach by isochoric (constant volume) freezing. International Journal of Food Science and Technology. 55(5):2141–2151.

Interpretive Summary: Isochoric freezing is a new preservation technique that preserves food products at subfreezing temperatures without the formation of ice crystals inside the products. Once the spinach leaves are cut from the plant, the leaves undergo senescence processes and oxidative stresses associated with wounding. Preserving the spinach at subfreezing temperatures under isochoric conditions can minimize the effects of wounding stress by reducing respiration, oxidation and enzymatic activities. These leaves maintain a fresh-like appearance with a firm and crunchy texture.

Technical Abstract: Efforts are currently directed towards improving the quality of vegetables after freezing and thawing. One of the methods under investigation is isochoric freezing. In this study, we evaluated isochoric freezing for preserving the quality of baby-leaf spinach. We examined their physico-chemical characteristics and nutritional value during one week of storage. We compared the properties of thawed spinach frozen to -4°C in an isochoric system with those of fresh spinach, thawed spinach frozen to -4ºC in an isobaric system and thawed spinach commercially frozen. Spinach leaves frozen under isobaric conditions and commercially frozen leaves lost mass and thickness, making them softer and translucent. They also lost much of their nutrient content. These samples were frozen under atmospheric pressure, which destroyed cell compartmentalization due to ice crystals formation. This might have amplified undesirable enzymatic reactions due to the release of the enzymes that came into contact with their substrates. In comparison, isochoric freezing maintained cell integrity and turgidity. Thawed leaves remained crunchy with characteristics similar to fresh leaves. Isochoric freezing also preserved nutritional content better than other systems, although significant nutrient losses still occurred. The metabolic reactions in cut spinach leaves might have been delayed and chemical reactions minimized under isochoric conditions.