Spinach packing for RTE products:
Ready-to-eat (RTE) leafy vegetables are the fastest increasing sector of the UK and Europe markets. Spinach (Spinacia oleracea) is one of the main leafy vegetables contributing to the RTE industry. Due to its tender and soft texture, spinach leaves tend to undergo different degrees of injuries during processing steps which affect their quality and shelf life. In this study, the effect of compression on quality degradation of spinach leaves during storage was investigated. Spinach leaves were subjected to compression using Universal Testing Machine where Young’s modulus for spinach in bulk amount; imitating packaged spinach in the industry was evaluated. Visual appearance was assessed by Population test where leaves were classified into categories according to degree of damage and percentage of deterioration was evaluated by analyzing RGB images using ImageJ. To understand the behavior better, microstructural property of the spinach was observed under light microscope. Organic spinach was found to be the best in resisting stress and damage compared to Teen, Salad and Baby spinach. Reducing weight of spinach inside the packaging bag, while putting appropriate weight reduced the possibility of the leaves inside the bag to be compressed due to the crowdedness inside the bag thus lowered the risk for accidental mechanical leaf damage. Including already broken leaves inside the packaging bag together with good leaves accelerates the deterioration of the whole leaves inside the bag. Halfway and complete teared leaves were found to be not acceptable to eat after 8 days of storage whereas control, undamaged and minor teared leaves were still acceptable to eat after 14 days of storage. The mechanical stress gave significant effect on the physical quality and mechanical property of spinach. Increasing the compression force did not change the cell sizes but changed the structure of the cells. This work provide basis to understand the physical quality and mechanical property of bulk spinach which can be used to improve the quality and shelf life of the packaged RTE spinach throughout the distribution chain.
The feasibility of RTE product such as spinach has great influence on consumers’ choices as it helps to reduce
preparation time before eating, apart from having such high nutritional values [1]. It has tender and soft texture which
can easily lead to damage. Before ready to be marketed, the RTE spinach bags undergone series of actions. Stacking
the bags, piling the trays, grabbing the bags and throwing the bags are examples of actions that caused the spinach
leaves inside the bag to be accidentally compressed, causing the leaves inside to be mechanically broken and damaged.
The mechanical damage will elevate the rate of decay of the products thus affect the sensorial and nutritional qualities
of the salads, which might lead the product to be inappropriate for the consumers’ consumptions [2]. The opened-cut
leaves exposed themselves to senescence process and oxidative stress, which then cause the accumulation of reactive
oxygen species (ROS). ROS is significant in maintaining abiotic stress response and physiological process in plants.
However, during oxidative stress, when ROS level increase dramatically, it can lead to significant damage to the cell
structures [1]. The external forces exerted on the plant caused mechanical injuries which then lead to changes of
texture, color, flavor, physiological, biochemical, and chemical composition of the commodities. Mechanical injuries
are irreversible plastic deformations that lead to organ breaking which then lead to cellular and tissue ruptures within
the plant [3, 4].
Young’s modulus, E is an intrinsic property of a material. Elastic and plastic deformation components of a material
are assumed to follow these two fundamental parameters: an elastic modulus and a “resistance to plastic deformation”.
In hard and compact material such as metal, the elastic deformation is minimal due to the relatively small resistance
to plastic deformation thus hardness can be measured by the resistance of the plastic deformation. In most other
materials including mineralized tissues, both elastic and plastic deformations contribute equally to the total
deformation, thus the hardness of the material is dependent on the elastic modulus, E. [5].
Many works on mechanical properties of different commodities have been reported.
SPINACH PACKING SYSTEMS:
Spanish iceberg (SI) had the range of E values from 1.1 - 2.0 MPa and 2.3 MPa - 4.4 MPa for ER and SI respectively
depending on the orientations of the sample position during the test [6]. Leaves (Calophyllum inophyllum L.) have E
values range from 186.4 – 240.2 MPa and 49.8 – 67.5 MPa when tested along and across the veins respectively [7].
Under compression test, potato was found to have range of E values from 3 to 6 MPa depending on the turgidity [8].
Studies on the mechanical properties for yucca, apple and pear also had been reported [9]. The E values for baby
spinach under tensile test in diagonal, perpendicular, and parallel directions were reported to be 1.084MPa, 0.3914
MPa and 2.137MPa respectively [2].
Although there has been work reported on the mechanical property of spinach, there is still lack of study to
determine the mechanical property of spinach in bulk amount; imitating the packaging bags of RTE spinach in the
industry. Most mechanical properties reported from the literature were performed onto individual materials not in bulk
amount; by performing mechanical tests such as tensile test, compression test, cutting, tearing, and shearing. Basic
data on the mechanical property of bulk spinach treated under various conditions was not available in the literature.
Study on the mechanical property of bulk spinach is necessary in order to improve the distribution chain of the
packaged RTE spinach thus improving the quality and shelf life of the products. Therefore, in this study, the
measurement of the mechanical property of bulk spinach was conducted by performing compression test where E
values and bulk densities were evaluated. Different leaf injuries were assessed by Population test, where the leaves
were group into degrees of injuries and the microstructures of the leaves were observed under the light microscope.
Spinach is a versatile vegetable that can be added to so many dishes and recipes for a boost of green goodness. Plus, it is something many people in many places can easily find at their grocery store all year round.
It is one vegetable I always have on hand for quick veggie-loading and is in many of my recipes. (check out spinach-loaded recipes for kids)
However, a question that I often have sliding into my email and DMs on Instagram is how to properly store spinach so that it doesn’t wilt or get mushy in just a few days.
I don’t know about you, but shopping every few days isn’t something I have time for. So keeping the spinach I get during my weekly stock up fresh is a must for making sure I have a staple family veggie on hand for meals.
Why does spinach go bad so quickly?
Moisture.
Veggies by nature have a high water content (how much varies from vegetable to vegetable), so when it comes to how to store spinach so that it stays fresh, we are working on keeping the moisture in the container you are storing the spinach in as minimal as possible.
Spinach types used in this experiment were Teen spinach, Organic spinach, Salad spinach supplied by Vitacress
UK from the same batch production and Baby spinach purchased from local supermarket in Birmingham, UK. While
choosing the spinach bags from the market, similarity of the production date and shelf life between each bags were
assured. All spinach bags were transported to the School of Chemical Engineering, University of Birmingham, where
the experiment was taking place. During the transportation, the spinach bags were stored inside cool bags with aid of
cool packs in order to minimise moisture loss of the spinach to the surrounding. Sorting of the leaves was done
manually and carefully to select good leaves only for the experiment. Good spinach leaves referred to the leaf that had
no breakage or damage, no disease, and also no discoloration (yellowing or browning). Apart from that, choosing a
standard size of the spinach leaves was also taken into account. Spinach bags that required storage were stored in cold
room with temperature 10±1°C.
SPINACH PACKING AUSTRALIA
The total volume of the Australian crop was 37,000 tonnes in 2018, which is up about 20 per cent in a year.
But Australian production is falling short of demand because it is a tricky vegetable to harvest.
It can grow year-round in Gippsland's Mitchell Valley, but it has to be picked at night or the leaf size gets too big to meet supermarket specifications.
Harvesters work in all conditions and have to cut the spinach very close to the ground.
"We basically use a bandsaw blade — like you'd find in a butcher's shop — attached to harvest machinery and you mow it off," he said.
"You've only got a few millimetres that you're playing with, between contacting the soil and picking the product at the right length."
Two harvest machines in a field at Lindenow in Gippsland harvesting spinach.
Harvesting spinach is like mowing grass. It is tricky to cut it without damaging the crop or picking up soil.(ABC Rural: David Claughton)
The Bulmer farm has struggled with labour shortages, and now sources 60 per cent of its staff from all over the Pacific and South-East Asia.
"We've got people coming Vanuatu, Timor Leste and from Kiribati."
Despite the shortfall in local workers and the increase in the award wages for casual staff, Mr Bulmer is optimistic about the future.
"The growth's been really good over the years, but we still lag behind other parts of the world when you look at household penetration," he said.
An average household in the United Kingdom makes 15–16 purchases of spinach a year, compared to Australia's 8–10 bags a year.
Powdered spinach
Global financial advice firm KPMG has looked at the opportunities for spinach globally.
Head of markets and agri-food tech sector Ben van Delden said the development of export hubs at regional airports in Toowoomba in Queensland and western Sydney could drive big growth into markets in South-East Asia.
"We're seeing a lot of investment in Australia to create 'agri-ports', very similar to the Netherlands model, where you've got infrastructure for food processing, packaging and customs logistics in the one place," Mr van Delden said.
Uniaxial compression
The compression test was performed using the Universal testing machine Z030 mechanical tester (Zwick/Roell,
UK). The samples were placed inside an acrylic chamber and undergone uniaxial compression by upper platon.
Compressibility or hardness of the spinach leaves was measured by a single cycle compression loading/unloading test.
Parameters that had been tested were compression forces, sample weight, types of spinach leaves, size of spinach
leaves (cut or whole leaves), and storage days. For every conditions tested, they were three to five times replications
for reproducibility purpose. Force-displacement curves were generated from TestExpertII software. From the raw
data, bulk density of the samples and Young’s modulus which was derived from the work and the bed volume of the
bulk samples under compression were calculated.
2.3. Population test
The compressed spinach leaves were assessed and number of damaged leaves were counted and classified into four
categories as described in Table 2. The classified leaves were packed inside normal packaging bags used for spinach
in industry;